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Merge remote-tracking branch 'origin/json-view/11-view-access' into HEAD

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Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-10-04 17:20:19 +02:00
parent f17207377b 5286c2843b
commit 0b6a55ea6b
118 changed files with 10341 additions and 3274 deletions
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docs/mkdocs/docs/api/basic_json/as_base_class.md
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@@ -0,0 +1,53 @@
# <small>nlohmann::basic_json::</small>as_base_class
```cpp
json_base_class_t& as_base_class() noexcept;
const json_base_class_t& as_base_class() const noexcept;
```
Returns a reference to this object as its custom base class [`json_base_class_t`](json_base_class_t.md). No copy is
made.
Since `basic_json` derives from `json_base_class_t`, a member of `basic_json` hides any member of the custom base class
with the same name. This function makes such hidden members accessible again.
## Return value
reference to this object as [`json_base_class_t`](json_base_class_t.md)
## Exception safety
No-throw guarantee: this function never throws exceptions.
## Complexity
Constant.
## Notes
The function is equivalent to `static_cast<json_base_class_t&>(j)` (or `static_cast<const json_base_class_t&>(j)`).
## Examples
??? example
The example shows how to use `as_base_class` to access members of the custom base class that are hidden by members
of `basic_json`.
```cpp
--8<-- "examples/as_base_class.cpp"
```
Output:
```json
--8<-- "examples/as_base_class.output"
```
## See also
- [json_base_class_t](json_base_class_t.md) - type of the custom base class
## Version history
- Added in version 3.13.0.
docs/mkdocs/docs/api/basic_json/at.md
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@@ -239,5 +239,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
1. Added in version 1.0.0.
2. Added in version 1.0.0.
3. Added in version 3.11.0.
3. Added in version 3.11.0. Fixed in version 3.13.0 to consistently accept `std::string_view`-convertible keys, as
already supported by [`operator[]`](operator[].md), [`value`](value.md), [`find`](find.md), and other lookup
functions.
4. Added in version 2.0.0.
docs/mkdocs/docs/api/basic_json/basic_json.md
+11 -1
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@@ -293,6 +293,15 @@ basic_json(basic_json&& other) noexcept;
When used without parentheses around an empty initializer list, `basic_json()` is called instead of this
function, yielding the JSON `#!json null` value.
- Overload 4:
!!! info "Implicit conversion"
The conversion is implicit unless [`JSON_USE_IMPLICIT_CONVERSIONS`](../macros/json_use_implicit_conversions.md)
is defined to `0` and `BasicJsonType::string_t` differs from `string_t`. In that case, the constructor is
`explicit`, so a JSON value with a different string type is no longer silently converted, for example when it is
passed to a function taking `#!cpp const json&`. Write `#!cpp json(other)` or `#!cpp other.get<json>()` instead.
- Overload 7:
!!! info "Preconditions"
@@ -466,7 +475,8 @@ basic_json(basic_json&& other) noexcept;
1. Since version 1.0.0.
2. Since version 1.0.0.
3. Since version 2.1.0.
4. Since version 3.2.0.
4. Since version 3.2.0. Explicit for different string types if `JSON_USE_IMPLICIT_CONVERSIONS` is `0` since
version 3.13.0.
5. Since version 1.0.0.
6. Since version 1.0.0.
7. Since version 1.0.0. Fixed in version 3.13.0 to also check the iterator range for binary values; before, a range
docs/mkdocs/docs/api/basic_json/contains.md
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@@ -132,7 +132,9 @@ Logarithmic in the size of the JSON object.
## Version history
1. Added in version 3.11.0.
2. Added in version 3.6.0. Extended template `KeyType` to support comparable types in version 3.11.0.
2. Added in version 3.6.0. Extended template `KeyType` to support comparable types in version 3.11.0. Fixed in
version 3.13.0 to consistently accept `std::string_view`-convertible keys, as already supported by
[`operator[]`](operator[].md), [`at`](at.md), [`value`](value.md), and other lookup functions.
3. Added in version 3.7.0.
4. Deleted overloads for integral key types added in version 3.13.0 to reject such calls at compile time instead of
causing undefined behavior at runtime.
docs/mkdocs/docs/api/basic_json/count.md
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@@ -85,6 +85,8 @@ Logarithmic in the size of the JSON object.
## Version history
1. Added in version 3.11.0.
2. Added in version 1.0.0. Changed parameter `key` type to `KeyType&&` in version 3.11.0.
2. Added in version 1.0.0. Changed parameter `key` type to `KeyType&&` in version 3.11.0. Fixed in version 3.13.0 to
consistently accept `std::string_view`-convertible keys, as already supported by [`operator[]`](operator[].md),
[`at`](at.md), [`value`](value.md), and other lookup functions.
3. Deleted overload for integral key types added in version 3.13.0 to reject such calls at compile time instead of
causing undefined behavior at runtime.
docs/mkdocs/docs/api/basic_json/dump.md
+6 -3
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@@ -25,10 +25,12 @@ and `ensure_ascii` parameters.
result consists of ASCII characters only.
`error_handler` (in)
: how to react on decoding errors; there are three possible values (see [`error_handler_t`](error_handler_t.md):
: how to react on decoding errors; there are four possible values (see [`error_handler_t`](error_handler_t.md):
`strict` (throws an exception in case a decoding error occurs; default), `replace` (replace invalid UTF-8 sequences
with U+FFFD), and `ignore` (ignore invalid UTF-8 sequences during serialization; all valid bytes are copied to the
output unchanged, and invalid bytes are dropped)).
with U+FFFD), `ignore` (ignore invalid UTF-8 sequences during serialization; all valid bytes are copied to the
output unchanged, and invalid bytes are dropped), and `keep` (write the ill-formed bytes to the output as is,
without escaping them, even if `ensure_ascii` is `#!cpp true`; the result is then not valid UTF-8, but equals the
input bytes exactly, and well-formed characters around the ill-formed bytes are still escaped as usual)).
## Return value
@@ -94,3 +96,4 @@ Binary values are serialized as an object containing two keys:
- Indentation character `indent_char`, option `ensure_ascii` and exceptions added in version 3.0.0.
- Error handlers added in version 3.4.0.
- Serialization of binary values added in version 3.8.0.
- Error handler `keep` added in version 3.13.0.
docs/mkdocs/docs/api/basic_json/emplace.md
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@@ -70,3 +70,5 @@ Logarithmic in the size of the container, O(log(`size()`)).
## Version history
- Since version 2.0.8.
- Fixed in version 3.13.0: for [`ordered_json`](../ordered_json.md), the value could previously only be passed as an
rvalue; it can now also be passed as an lvalue or a `#!cpp const` lvalue, matching the behavior of `json`.
docs/mkdocs/docs/api/basic_json/erase.md
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@@ -213,5 +213,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
1. Added in version 1.0.0. Added support for binary types in version 3.8.0.
2. Added in version 1.0.0. Added support for binary types in version 3.8.0.
3. Added in version 1.0.0.
4. Added in version 3.11.0.
4. Added in version 3.11.0. Fixed in version 3.13.0 to consistently accept `std::string_view`-convertible keys, as
already supported by [`operator[]`](operator[].md), [`at`](at.md), [`value`](value.md), and other lookup
functions.
5. Added in version 1.0.0.
docs/mkdocs/docs/api/basic_json/error_handler_t.md
+28 -4
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@@ -4,15 +4,31 @@
enum class error_handler_t {
strict,
replace,
ignore
ignore,
keep
};
```
This enumeration is used in the [`dump`](dump.md) function to choose how to treat decoding errors while serializing a
`basic_json` value. Three values are differentiated:
This enumeration is used to choose how to treat ill-formed UTF-8 in a string value or object key:
- [`dump`](dump.md) uses it while serializing a `basic_json` value to text.
- [`to_cbor`](to_cbor.md), [`to_msgpack`](to_msgpack.md), [`to_ubjson`](to_ubjson.md), [`to_bjdata`](to_bjdata.md),
and [`to_bson`](to_bson.md) use it while serializing a `basic_json` value to that binary format. Their default is
`keep`, as no binary writer checked before this parameter was added. CBOR, UBJSON, BJData, and BSON require valid
UTF-8, so for these four the default is `strict` if [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md)
is enabled; MessagePack's specification explicitly allows a string to contain ill-formed UTF-8, so `to_msgpack`
stays at `keep`. `to_bon8` does not take this parameter: BON8 always validates, since UTF-8 lead bytes are
structural to that format.
- [`from_cbor`](from_cbor.md), [`from_msgpack`](from_msgpack.md), [`from_ubjson`](from_ubjson.md),
[`from_bjdata`](from_bjdata.md), and [`from_bson`](from_bson.md) use it while parsing that binary format, to decide
whether to check a string value or object key for well-formed UTF-8 at all; by default (`keep`) they do not, as no
binary reader did before this parameter was added. `from_bon8` does not take this parameter, for the same reason
`to_bon8` does not.
Four values are differentiated:
strict
: throw a `type_error` exception in case of invalid UTF-8
: throw a `type_error`/`parse_error` exception in case of invalid UTF-8
replace
: replace invalid UTF-8 sequences with U+FFFD (� REPLACEMENT CHARACTER)
@@ -20,6 +36,12 @@ replace
ignore
: ignore invalid UTF-8 sequences; all valid bytes are copied to the output unchanged, and invalid bytes are dropped
keep
: keep invalid UTF-8 sequences unchanged; only meaningful for the binary formats mentioned above, since [`dump`]
(dump.md) itself must produce text, and `keep` there writes the ill-formed bytes to the output as is, so the
result is then not valid UTF-8 (but still equals the input bytes exactly, including around any well-formed
characters, which are still escaped as usual)
## Examples
??? example
@@ -45,3 +67,5 @@ ignore
## Version history
- Added in version 3.4.0.
- Added `keep`, and made this enumeration apply to the binary readers and writers in addition to `dump`, in version
3.13.0.
docs/mkdocs/docs/api/basic_json/find.md
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@@ -89,6 +89,8 @@ Logarithmic in the size of the JSON object.
## Version history
1. Added in version 3.11.0.
2. Added in version 1.0.0. Changed to support comparable types in version 3.11.0.
2. Added in version 1.0.0. Changed to support comparable types in version 3.11.0. Fixed in version 3.13.0 to
consistently accept `std::string_view`-convertible keys, as already supported by [`operator[]`](operator[].md),
[`at`](at.md), [`value`](value.md), and other lookup functions.
3. Deleted overloads for integral key types added in version 3.13.0 to reject such calls at compile time instead of
causing undefined behavior at runtime.
docs/mkdocs/docs/api/basic_json/from_bjdata.md
+12 -3
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@@ -5,12 +5,14 @@
template<typename InputType>
static basic_json from_bjdata(InputType&& i,
const bool strict = true,
const bool allow_exceptions = true);
const bool allow_exceptions = true,
const error_handler_t error_handler = error_handler_t::keep);
// (2)
template<typename IteratorType, typename SentinelType = IteratorType>
static basic_json from_bjdata(IteratorType first, SentinelType last,
const bool strict = true,
const bool allow_exceptions = true);
const bool allow_exceptions = true,
const error_handler_t error_handler = error_handler_t::keep);
```
Deserializes a given input to a JSON value using the BJData (Binary JData) serialization format.
@@ -58,6 +60,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
`allow_exceptions` (in)
: whether to throw exceptions in case of a parse error (optional, `#!cpp true` by default)
`error_handler` (in)
: how to treat a string value or object key that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
BJData does not require a decoder to reject ill-formed UTF-8, so checking is opt-in: the default, `keep`, does not
check at all, as every binary reader did before this parameter was added; `strict` checks and throws;
`replace`/`ignore` sanitize the string the same way [`dump`](dump.md) would
## Return value
deserialized JSON value; in case of a parse error and `allow_exceptions` set to `#!cpp false`, the return value will be
@@ -73,7 +81,7 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
the end of the file was not reached when `strict` was set to true
- Throws [parse_error.112](../../home/exceptions.md#jsonexceptionparse_error112) if a parse error occurs
- Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a string could not be parsed
successfully
successfully, or if a string value or object key is not valid UTF-8 and `error_handler` is `strict`
- Throws [out_of_range.408](../../home/exceptions.md#jsonexceptionout_of_range408) if the size of an optimized container
or n-dimensional array cannot be represented by `std::size_t`
@@ -111,3 +119,4 @@ Linear in the size of the input.
- Added in version 3.11.0.
- Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
- Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
- Added `error_handler` parameter in version 3.13.0.
docs/mkdocs/docs/api/basic_json/from_bson.md
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@@ -5,12 +5,14 @@
template<typename InputType>
static basic_json from_bson(InputType&& i,
const bool strict = true,
const bool allow_exceptions = true);
const bool allow_exceptions = true,
const error_handler_t error_handler = error_handler_t::keep);
// (2)
template<typename IteratorType, typename SentinelType = IteratorType>
static basic_json from_bson(IteratorType first, SentinelType last,
const bool strict = true,
const bool allow_exceptions = true);
const bool allow_exceptions = true,
const error_handler_t error_handler = error_handler_t::keep);
```
Deserializes a given input to a JSON value using the BSON (Binary JSON) serialization format.
@@ -58,6 +60,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
`allow_exceptions` (in)
: whether to throw exceptions in case of a parse error (optional, `#!cpp true` by default)
`error_handler` (in)
: how to treat a string value or object key that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
BSON does not require a decoder to reject ill-formed UTF-8, so checking is opt-in: the default, `keep`, does not
check at all, as every binary reader did before this parameter was added; `strict` checks and throws;
`replace`/`ignore` sanitize the string the same way [`dump`](dump.md) would
## Return value
deserialized JSON value; in case of a parse error and `allow_exceptions` set to `#!cpp false`, the return value will be
@@ -75,6 +83,8 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
invalid string or byte array length)
- Throws [`parse_error.114`](../../home/exceptions.md#jsonexceptionparse_error114) if an unsupported BSON record type is
encountered
- Throws [`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) if a string value or object key is
not valid UTF-8 and `error_handler` is `strict`
## Complexity
@@ -111,6 +121,7 @@ Linear in the size of the input.
- Added in version 3.4.0.
- Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
- Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
- Added `error_handler` parameter in version 3.13.0.
!!! warning "Deprecation"
docs/mkdocs/docs/api/basic_json/from_cbor.md
+14 -4
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@@ -6,14 +6,16 @@ template<typename InputType>
static basic_json from_cbor(InputType&& i,
const bool strict = true,
const bool allow_exceptions = true,
const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error);
const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error,
const error_handler_t error_handler = error_handler_t::keep);
// (2)
template<typename IteratorType, typename SentinelType = IteratorType>
static basic_json from_cbor(IteratorType first, SentinelType last,
const bool strict = true,
const bool allow_exceptions = true,
const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error);
const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error,
const error_handler_t error_handler = error_handler_t::keep);
```
Deserializes a given input to a JSON value using the CBOR (Concise Binary Object Representation) serialization format.
@@ -65,6 +67,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
: how to treat CBOR tags (optional, `error` by default); see [`cbor_tag_handler_t`](cbor_tag_handler_t.md) for more
information
`error_handler` (in)
: how to treat a string value or object key that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
CBOR does not require a decoder to reject ill-formed UTF-8, so checking is opt-in: the default, `keep`, does not
check at all, as every binary reader did before this parameter was added; `strict` checks and throws;
`replace`/`ignore` sanitize the string the same way [`dump`](dump.md) would
## Return value
deserialized JSON value; in case of a parse error and `allow_exceptions` set to `#!cpp false`, the return value will be
@@ -80,8 +88,9 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
the end of the file was not reached when `strict` was set to true
- Throws [parse_error.112](../../home/exceptions.md#jsonexceptionparse_error112) if unsupported features from CBOR were
used in the given input or if the input is not valid CBOR
- Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a map key is not a string (keys of other
types are not supported, as JSON object keys are always strings) or a string is malformed
- Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a map key is not a string (keys of
other types are not supported, as JSON object keys are always strings), or if a string value or object key is not
valid UTF-8 and `error_handler` is `strict`
## Complexity
@@ -121,6 +130,7 @@ Linear in the size of the input.
- Added `tag_handler` parameter in version 3.9.0.
- Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
- Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
- Added `error_handler` parameter in version 3.13.0.
!!! warning "Deprecation"
docs/mkdocs/docs/api/basic_json/from_msgpack.md
+14 -4
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@@ -5,12 +5,14 @@
template<typename InputType>
static basic_json from_msgpack(InputType&& i,
const bool strict = true,
const bool allow_exceptions = true);
const bool allow_exceptions = true,
const error_handler_t error_handler = error_handler_t::keep);
// (2)
template<typename IteratorType, typename SentinelType = IteratorType>
static basic_json from_msgpack(IteratorType first, SentinelType last,
const bool strict = true,
const bool allow_exceptions = true);
const bool allow_exceptions = true,
const error_handler_t error_handler = error_handler_t::keep);
```
Deserializes a given input to a JSON value using the MessagePack serialization format.
@@ -58,6 +60,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
`allow_exceptions` (in)
: whether to throw exceptions in case of a parse error (optional, `#!cpp true` by default)
`error_handler` (in)
: how to treat a string value or object key that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
MessagePack's specification explicitly allows ill-formed UTF-8, so checking is opt-in: the default, `keep`, does
not check at all, as every binary reader did before this parameter was added; `strict` checks and throws;
`replace`/`ignore` sanitize the string the same way [`dump`](dump.md) would
## Return value
deserialized JSON value; in case of a parse error and `allow_exceptions` set to `#!cpp false`, the return value will be
@@ -73,8 +81,9 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
the end of the file was not reached when `strict` was set to true
- Throws [parse_error.112](../../home/exceptions.md#jsonexceptionparse_error112) if unsupported features from
MessagePack were used in the given input or if the input is not valid MessagePack
- Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a map key is not a string (keys of other
types are not supported, as JSON object keys are always strings) or a string is malformed
- Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a map key is not a string (keys of
other types are not supported, as JSON object keys are always strings), or if a string value or object key is not
valid UTF-8 and `error_handler` is `strict`
## Complexity
@@ -113,6 +122,7 @@ Linear in the size of the input.
- Added `allow_exceptions` parameter in version 3.2.0.
- Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
- Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
- Added `error_handler` parameter in version 3.13.0.
!!! warning "Deprecation"
docs/mkdocs/docs/api/basic_json/from_ubjson.md
+12 -3
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@@ -5,12 +5,14 @@
template<typename InputType>
static basic_json from_ubjson(InputType&& i,
const bool strict = true,
const bool allow_exceptions = true);
const bool allow_exceptions = true,
const error_handler_t error_handler = error_handler_t::keep);
// (2)
template<typename IteratorType, typename SentinelType = IteratorType>
static basic_json from_ubjson(IteratorType first, SentinelType last,
const bool strict = true,
const bool allow_exceptions = true);
const bool allow_exceptions = true,
const error_handler_t error_handler = error_handler_t::keep);
```
Deserializes a given input to a JSON value using the UBJSON (Universal Binary JSON) serialization format.
@@ -58,6 +60,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
`allow_exceptions` (in)
: whether to throw exceptions in case of a parse error (optional, `#!cpp true` by default)
`error_handler` (in)
: how to treat a string value or object key that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
UBJSON does not require a decoder to reject ill-formed UTF-8, so checking is opt-in: the default, `keep`, does not
check at all, as every binary reader did before this parameter was added; `strict` checks and throws;
`replace`/`ignore` sanitize the string the same way [`dump`](dump.md) would
## Return value
deserialized JSON value; in case of a parse error and `allow_exceptions` set to `#!cpp false`, the return value will be
@@ -73,7 +81,7 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
the end of the file was not reached when `strict` was set to true
- Throws [parse_error.112](../../home/exceptions.md#jsonexceptionparse_error112) if a parse error occurs
- Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a string could not be parsed
successfully
successfully, or if a string value or object key is not valid UTF-8 and `error_handler` is `strict`
- Throws [out_of_range.408](../../home/exceptions.md#jsonexceptionout_of_range408) if the size of an optimized container
or n-dimensional array cannot be represented by `std::size_t`
@@ -112,6 +120,7 @@ Linear in the size of the input.
- Added `allow_exceptions` parameter in version 3.2.0.
- Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
- Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
- Added `error_handler` parameter in version 3.13.0.
!!! warning "Deprecation"
docs/mkdocs/docs/api/basic_json/index.md
+1
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@@ -200,6 +200,7 @@ Direct access to the stored value of a JSON value.
- [**get_ref**](get_ref.md) - get a reference value
- [**operator ValueType**](operator_ValueType.md) - get a value
- [**get_binary**](get_binary.md) - get a binary value
- [**as_base_class**](as_base_class.md) - access the custom base class
### Element access
docs/mkdocs/docs/api/basic_json/json_base_class_t.md
+14
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@@ -27,6 +27,18 @@ A `CustomBaseClass` with non-static data members forfeits `basic_json`'s
[standard layout](https://en.cppreference.com/w/cpp/named_req/StandardLayoutType) guarantee. See
[Template Parameter Requirements](../../features/types/template_parameters.md#custombaseclass).
#### Name conflicts
Since `basic_json` derives from `CustomBaseClass`, members of `basic_json` hide members of `CustomBaseClass` with the
same name. Hidden members remain accessible via [`as_base_class`](as_base_class.md) or by casting the value to
`json_base_class_t`.
!!! warning "Avoid generic member names"
Future versions of the library may add members to `basic_json` that hide members of `CustomBaseClass` that are
accessible today. To reduce the risk of such conflicts, avoid generic names for the members of `CustomBaseClass`,
for instance by using a distinctive prefix.
## Examples
??? example
@@ -45,8 +57,10 @@ A `CustomBaseClass` with non-static data members forfeits `basic_json`'s
## See also
- [as_base_class](as_base_class.md) - access the custom base class
- [Template Parameter Requirements](../../features/types/template_parameters.md#custombaseclass) - the requirements for `CustomBaseClass`
## Version history
- Added in version 3.12.0.
- Made a public member type in version 3.13.0; it was private before, so it could not be named outside the class.
docs/mkdocs/docs/api/basic_json/meta.md
+1 -1
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@@ -13,7 +13,7 @@ JSON object holding version information
| key | description |
|-------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| `compiler` | Information on the used compiler. It is an object with the following keys: `c++` (the used C++ standard), `family` (the compiler family; possible values are `clang`, `icc`, `gcc`, `ilecpp`, `msvc`, `pgcpp`, `sunpro`, and `unknown`), and `version` (the compiler version). On HP aCC compilers, `compiler` is instead the plain string `hp`. |
| `compiler` | Information on the used compiler. It is an object with the following keys: `c++` (the used C++ standard), `family` (the compiler family; possible values are `clang`, `icc`, `gcc`, `hp`, `ilecpp`, `msvc`, `pgcpp`, `sunpro`, and `unknown`), and `version` (the compiler version). |
| `copyright` | The copyright line for the library as string. |
| `name` | The name of the library as string. |
| `platform` | The used platform as string. Possible values are `win32`, `linux`, `apple`, `unix`, and `unknown`. |
docs/mkdocs/docs/api/basic_json/operator[].md
+11 -3
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@@ -89,6 +89,9 @@ Strong exception safety: if an exception occurs, the original value stays intact
- Throws [`out_of_range.410`](../../home/exceptions.md#jsonexceptionout_of_range410) if an array index in the passed
JSON pointer `ptr` exceeds the range of `size_type` (e.g., on 32-bit platforms).
For the **const** version, an object key or array index in `ptr` that does not exist is not reported by an
exception, but is undefined behavior (see the notes below). Use [`at`](at.md) for checked access.
## Complexity
1. Constant if `idx` is in the range of the array. Otherwise, linear in `idx - size()`.
@@ -103,9 +106,12 @@ Strong exception safety: if an exception occurs, the original value stays intact
The following cases apply to the **const** overloads; the non-const overloads instead insert the missing element
(see the notes below).
1. If the element at index `idx` does not exist, the behavior is undefined.
1. If the element at index `idx` does not exist, the behavior is undefined and is **guarded by a
[runtime assertion](../../features/assertions.md)**!
2. If the element with key `key` does not exist, the behavior is undefined and is **guarded by a
[runtime assertion](../../features/assertions.md)**!
3. If the JSON pointer `ptr` refers to an object key or an array index that does not exist, the behavior is
undefined and is **guarded by a [runtime assertion](../../features/assertions.md)**!
1. The non-const version may add values: If `idx` is beyond the range of the array (i.e., `idx >= size()`), then the
array is silently filled up with `#!json null` values to make `idx` a valid reference to the last stored element. In
@@ -275,9 +281,11 @@ Strong exception safety: if an exception occurs, the original value stays intact
## Version history
1. Added in version 1.0.0. Fixed in version 3.13.0 to throw `#!cpp std::length_error` instead of emptying the array and
accessing it out of bounds when `idx` equals the maximum value of `size_type`.
accessing it out of bounds when `idx` equals the maximum value of `size_type`. A missing index in the const version
is guarded by a runtime assertion since version 3.13.0.
2. Added in version 1.0.0. Added overloads for `T* key` in version 1.1.0. Removed overloads for `T* key` (replaced by 3)
in version 3.11.0.
3. Added in version 3.11.0. Fixed in version 3.13.0 to consistently accept `std::string_view`-convertible keys, as
already supported by [`at`](at.md), [`value`](value.md), [`find`](find.md), and other lookup functions.
4. Added in version 2.0.0.
4. Added in version 2.0.0. A missing array index in the const version is guarded by a runtime assertion since
version 3.13.0.
docs/mkdocs/docs/api/basic_json/operator_eq.md
+10 -4
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@@ -5,17 +5,17 @@
bool operator==(const_reference lhs, const_reference rhs) noexcept; // (1)
template<typename ScalarType>
bool operator==(const_reference lhs, const ScalarType rhs) noexcept; // (2)
bool operator==(const_reference lhs, const ScalarType rhs) noexcept(/* see below */); // (2)
template<typename ScalarType>
bool operator==(ScalarType lhs, const const_reference rhs) noexcept; // (2)
bool operator==(ScalarType lhs, const const_reference rhs) noexcept(/* see below */); // (2)
// since C++20
class basic_json {
bool operator==(const_reference rhs) const noexcept; // (1)
template<typename ScalarType>
bool operator==(ScalarType rhs) const noexcept; // (2)
bool operator==(ScalarType rhs) const noexcept(/* see below */); // (2)
};
```
@@ -46,7 +46,12 @@ whether the values `lhs`/`*this` and `rhs` are equal
## Exception safety
No-throw guarantee: this function never throws exceptions.
1. No-throw guarantee: this function never throws exceptions.
2. No-throw guarantee if converting the scalar to a JSON value cannot throw, as for numbers, Booleans, and
`#!cpp nullptr`; the function is `#!cpp noexcept` exactly in that case. Otherwise, it throws what the conversion
throws, for example `std::bad_alloc` when converting a string, or
[`out_of_range.410`](../../home/exceptions.md#jsonexceptionout_of_range410) for an enum value not mapped by
[`NLOHMANN_JSON_SERIALIZE_ENUM_STRICT`](../macros/nlohmann_json_serialize_enum_strict.md).
## Complexity
@@ -171,3 +176,4 @@ Linear.
1. Added in version 1.0.0. Added C++20 member functions in version 3.11.0.
2. Added in version 1.0.0. Added C++20 member functions in version 3.11.0.
Made conditionally `#!cpp noexcept` in version 3.13.0; before, a throwing conversion called `std::terminate`.
docs/mkdocs/docs/api/basic_json/operator_ge.md
+9 -3
View File
@@ -5,10 +5,10 @@
bool operator>=(const_reference lhs, const_reference rhs) noexcept; // (1)
template<typename ScalarType>
bool operator>=(const_reference lhs, const ScalarType rhs) noexcept; // (2)
bool operator>=(const_reference lhs, const ScalarType rhs) noexcept(/* see below */); // (2)
template<typename ScalarType>
bool operator>=(ScalarType lhs, const const_reference rhs) noexcept; // (2)
bool operator>=(ScalarType lhs, const const_reference rhs) noexcept(/* see below */); // (2)
```
1. Compares whether one JSON value `lhs` is greater than or equal to another JSON value `rhs` according to the following
@@ -39,7 +39,12 @@ whether `lhs` is greater than or equal to `rhs`
## Exception safety
No-throw guarantee: this function never throws exceptions.
1. No-throw guarantee: this function never throws exceptions.
2. No-throw guarantee if converting the scalar to a JSON value cannot throw, as for numbers, Booleans, and
`#!cpp nullptr`; the function is `#!cpp noexcept` exactly in that case. Otherwise, it throws what the conversion
throws, for example `std::bad_alloc` when converting a string, or
[`out_of_range.410`](../../home/exceptions.md#jsonexceptionout_of_range410) for an enum value not mapped by
[`NLOHMANN_JSON_SERIALIZE_ENUM_STRICT`](../macros/nlohmann_json_serialize_enum_strict.md).
## Complexity
@@ -94,3 +99,4 @@ Linear.
1. Added in version 1.0.0. Conditionally removed since C++20 in version 3.11.0.
2. Added in version 1.0.0. Conditionally removed since C++20 in version 3.11.0.
Made conditionally `#!cpp noexcept` in version 3.13.0; before, a throwing conversion called `std::terminate`.
docs/mkdocs/docs/api/basic_json/operator_gt.md
+9 -3
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@@ -5,10 +5,10 @@
bool operator>(const_reference lhs, const_reference rhs) noexcept; // (1)
template<typename ScalarType>
bool operator>(const_reference lhs, const ScalarType rhs) noexcept; // (2)
bool operator>(const_reference lhs, const ScalarType rhs) noexcept(/* see below */); // (2)
template<typename ScalarType>
bool operator>(ScalarType lhs, const const_reference rhs) noexcept; // (2)
bool operator>(ScalarType lhs, const const_reference rhs) noexcept(/* see below */); // (2)
```
1. Compares whether one JSON value `lhs` is greater than another JSON value `rhs` according to the
@@ -39,7 +39,12 @@ whether `lhs` is greater than `rhs`
## Exception safety
No-throw guarantee: this function never throws exceptions.
1. No-throw guarantee: this function never throws exceptions.
2. No-throw guarantee if converting the scalar to a JSON value cannot throw, as for numbers, Booleans, and
`#!cpp nullptr`; the function is `#!cpp noexcept` exactly in that case. Otherwise, it throws what the conversion
throws, for example `std::bad_alloc` when converting a string, or
[`out_of_range.410`](../../home/exceptions.md#jsonexceptionout_of_range410) for an enum value not mapped by
[`NLOHMANN_JSON_SERIALIZE_ENUM_STRICT`](../macros/nlohmann_json_serialize_enum_strict.md).
## Complexity
@@ -84,3 +89,4 @@ Linear.
1. Added in version 1.0.0. Conditionally removed since C++20 in version 3.11.0.
2. Added in version 1.0.0. Conditionally removed since C++20 in version 3.11.0.
Made conditionally `#!cpp noexcept` in version 3.13.0; before, a throwing conversion called `std::terminate`.
docs/mkdocs/docs/api/basic_json/operator_le.md
+9 -3
View File
@@ -5,10 +5,10 @@
bool operator<=(const_reference lhs, const_reference rhs) noexcept; // (1)
template<typename ScalarType>
bool operator<=(const_reference lhs, const ScalarType rhs) noexcept; // (2)
bool operator<=(const_reference lhs, const ScalarType rhs) noexcept(/* see below */); // (2)
template<typename ScalarType>
bool operator<=(ScalarType lhs, const const_reference rhs) noexcept; // (2)
bool operator<=(ScalarType lhs, const const_reference rhs) noexcept(/* see below */); // (2)
```
1. Compares whether one JSON value `lhs` is less than or equal to another JSON value `rhs`
@@ -40,7 +40,12 @@ whether `lhs` is less than or equal to `rhs`
## Exception safety
No-throw guarantee: this function never throws exceptions.
1. No-throw guarantee: this function never throws exceptions.
2. No-throw guarantee if converting the scalar to a JSON value cannot throw, as for numbers, Booleans, and
`#!cpp nullptr`; the function is `#!cpp noexcept` exactly in that case. Otherwise, it throws what the conversion
throws, for example `std::bad_alloc` when converting a string, or
[`out_of_range.410`](../../home/exceptions.md#jsonexceptionout_of_range410) for an enum value not mapped by
[`NLOHMANN_JSON_SERIALIZE_ENUM_STRICT`](../macros/nlohmann_json_serialize_enum_strict.md).
## Complexity
@@ -95,3 +100,4 @@ Linear.
1. Added in version 1.0.0. Conditionally removed since C++20 in version 3.11.0.
2. Added in version 1.0.0. Conditionally removed since C++20 in version 3.11.0.
Made conditionally `#!cpp noexcept` in version 3.13.0; before, a throwing conversion called `std::terminate`.
docs/mkdocs/docs/api/basic_json/operator_lt.md
+9 -3
View File
@@ -5,10 +5,10 @@
bool operator<(const_reference lhs, const_reference rhs) noexcept; // (1)
template<typename ScalarType>
bool operator<(const_reference lhs, const ScalarType rhs) noexcept; // (2)
bool operator<(const_reference lhs, const ScalarType rhs) noexcept(/* see below */); // (2)
template<typename ScalarType>
bool operator<(ScalarType lhs, const const_reference rhs) noexcept; // (2)
bool operator<(ScalarType lhs, const const_reference rhs) noexcept(/* see below */); // (2)
```
1. Compares whether one JSON value `lhs` is less than another JSON value `rhs` according to the
@@ -49,7 +49,12 @@ whether `lhs` is less than `rhs`
## Exception safety
No-throw guarantee: this function never throws exceptions.
1. No-throw guarantee: this function never throws exceptions.
2. No-throw guarantee if converting the scalar to a JSON value cannot throw, as for numbers, Booleans, and
`#!cpp nullptr`; the function is `#!cpp noexcept` exactly in that case. Otherwise, it throws what the conversion
throws, for example `std::bad_alloc` when converting a string, or
[`out_of_range.410`](../../home/exceptions.md#jsonexceptionout_of_range410) for an enum value not mapped by
[`NLOHMANN_JSON_SERIALIZE_ENUM_STRICT`](../macros/nlohmann_json_serialize_enum_strict.md).
## Complexity
@@ -94,3 +99,4 @@ Linear.
1. Added in version 1.0.0. Conditionally removed since C++20 in version 3.11.0.
2. Added in version 1.0.0. Conditionally removed since C++20 in version 3.11.0.
Made conditionally `#!cpp noexcept` in version 3.13.0; before, a throwing conversion called `std::terminate`.
docs/mkdocs/docs/api/basic_json/operator_ne.md
+9 -3
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@@ -5,10 +5,10 @@
bool operator!=(const_reference lhs, const_reference rhs) noexcept; // (1)
template<typename ScalarType>
bool operator!=(const_reference lhs, const ScalarType rhs) noexcept; // (2)
bool operator!=(const_reference lhs, const ScalarType rhs) noexcept(/* see below */); // (2)
template<typename ScalarType>
bool operator!=(ScalarType lhs, const const_reference rhs) noexcept; // (2)
bool operator!=(ScalarType lhs, const const_reference rhs) noexcept(/* see below */); // (2)
```
1. Compares two JSON values for inequality. Returns `#!cpp !(lhs == rhs)`.
@@ -36,7 +36,12 @@ whether the values `lhs`/`*this` and `rhs` are not equal
## Exception safety
No-throw guarantee: this function never throws exceptions.
1. No-throw guarantee: this function never throws exceptions.
2. No-throw guarantee if converting the scalar to a JSON value cannot throw, as for numbers, Booleans, and
`#!cpp nullptr`; the function is `#!cpp noexcept` exactly in that case. Otherwise, it throws what the conversion
throws, for example `std::bad_alloc` when converting a string, or
[`out_of_range.410`](../../home/exceptions.md#jsonexceptionout_of_range410) for an enum value not mapped by
[`NLOHMANN_JSON_SERIALIZE_ENUM_STRICT`](../macros/nlohmann_json_serialize_enum_strict.md).
## Complexity
@@ -98,3 +103,4 @@ Linear.
member function in version 3.13.0; since C++20, the compiler rewrites `a != b` using `operator==`.
2. Added in version 1.0.0. Changed in version 3.13.0 to remove special-casing for `NaN` and `discarded` values;
`operator!=` now consistently means `!(a == b)`. Since C++20, the compiler rewrites `a != b` using `operator==`.
Made conditionally `#!cpp noexcept` in version 3.13.0; before, a throwing conversion called `std::terminate`.
docs/mkdocs/docs/api/basic_json/operator_spaceship.md
+8 -2
View File
@@ -6,7 +6,7 @@ class basic_json {
std::partial_ordering operator<=>(const_reference rhs) const noexcept; // (1)
template<typename ScalarType>
std::partial_ordering operator<=>(const ScalarType rhs) const noexcept; // (2)
std::partial_ordering operator<=>(const ScalarType rhs) const noexcept(/* see below */); // (2)
};
```
@@ -39,7 +39,12 @@ the `std::partial_ordering` of the 3-way comparison of `*this` and `rhs`
## Exception safety
No-throw guarantee: this function never throws exceptions.
1. No-throw guarantee: this function never throws exceptions.
2. No-throw guarantee if converting the scalar to a JSON value cannot throw, as for numbers, Booleans, and
`#!cpp nullptr`; the function is `#!cpp noexcept` exactly in that case. Otherwise, it throws what the conversion
throws, for example `std::bad_alloc` when converting a string, or
[`out_of_range.410`](../../home/exceptions.md#jsonexceptionout_of_range410) for an enum value not mapped by
[`NLOHMANN_JSON_SERIALIZE_ENUM_STRICT`](../macros/nlohmann_json_serialize_enum_strict.md).
## Complexity
@@ -98,3 +103,4 @@ Linear.
1. Added in version 3.11.0.
2. Added in version 3.11.0.
Made conditionally `#!cpp noexcept` in version 3.13.0; before, a throwing conversion called `std::terminate`.
docs/mkdocs/docs/api/basic_json/to_bjdata.md
+19 -4
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@@ -5,15 +5,18 @@
static std::vector<std::uint8_t> to_bjdata(const basic_json& j,
const bool use_size = false,
const bool use_type = false,
const bjdata_version_t version = bjdata_version_t::draft2);
const bjdata_version_t version = bjdata_version_t::draft2,
const error_handler_t error_handler = error_handler_t::keep);
// (2)
static void to_bjdata(const basic_json& j, detail::output_adapter<std::uint8_t> o,
const bool use_size = false, const bool use_type = false,
const bjdata_version_t version = bjdata_version_t::draft2);
const bjdata_version_t version = bjdata_version_t::draft2,
const error_handler_t error_handler = error_handler_t::keep);
static void to_bjdata(const basic_json& j, detail::output_adapter<char> o,
const bool use_size = false, const bool use_type = false,
const bjdata_version_t version = bjdata_version_t::draft2);
const bjdata_version_t version = bjdata_version_t::draft2,
const error_handler_t error_handler = error_handler_t::keep);
```
Serializes a given JSON value `j` to a byte vector using the BJData (Binary JData) serialization format. BJData aims to
@@ -43,6 +46,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
: which version of BJData to use (see note on "Binary values" on [BJData](../../features/binary_formats/bjdata.md));
optional, `#!cpp bjdata_version_t::draft2` by default.
`error_handler` (in)
: how to treat a string or object key in `j` that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
The default, `keep`, writes the ill-formed bytes to the output as is, as every version of `to_bjdata` did before
this parameter was added; `strict` throws; `replace`/`ignore` sanitize it the same way [`dump`](dump.md) would.
If [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled, the default is `strict` instead.
## Return value
1. BJData serialization as byte vector
@@ -56,6 +65,9 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
- Throws [`other_error.502`](../../home/exceptions.md#jsonexceptionother_error502) if `use_type` is true and `use_size`
is false, and `j` contains a non-empty array, object, or binary value.
- Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key in `j` is
not valid UTF-8 and `error_handler` is `strict` (the default only if
[`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled)
## Complexity
@@ -104,4 +116,7 @@ Linear in the size of the JSON value `j`.
## Version history
- Added in version 3.11.0.
- BJData version parameter (for draft3 binary encoding) added in version 3.12.0.
- BJData version parameter (for draft3 binary encoding) added in version 3.12.0.
- Added `error_handler` parameter in version 3.13.0. Its default, `keep`, writes the bytes of a string or object key
that is not valid UTF-8 unchanged, as before; `strict` (the default if
[`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled) throws `type_error.316`.
docs/mkdocs/docs/api/basic_json/to_bson.md
+19 -3
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@@ -2,11 +2,14 @@
```cpp
// (1)
static std::vector<std::uint8_t> to_bson(const basic_json& j);
static std::vector<std::uint8_t> to_bson(const basic_json& j,
const error_handler_t error_handler = error_handler_t::keep);
// (2)
static void to_bson(const basic_json& j, detail::output_adapter<std::uint8_t> o);
static void to_bson(const basic_json& j, detail::output_adapter<char> o);
static void to_bson(const basic_json& j, detail::output_adapter<std::uint8_t> o,
const error_handler_t error_handler = error_handler_t::keep);
static void to_bson(const basic_json& j, detail::output_adapter<char> o,
const error_handler_t error_handler = error_handler_t::keep);
```
BSON (Binary JSON) is a binary format in which zero or more ordered key/value pairs are stored as a single entity (a
@@ -25,6 +28,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
`o` (in)
: output adapter to write serialization to
`error_handler` (in)
: how to treat a string or object key in `j` that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
The default, `keep`, writes the ill-formed bytes to the output as is, as every version of `to_bson` did before
this parameter was added; `strict` throws; `replace`/`ignore` sanitize it the same way [`dump`](dump.md) would.
If [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled, the default is `strict` instead.
## Return value
1. BSON serialization as a byte vector
@@ -46,6 +55,9 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
- Throws [`out_of_range.415`](../../home/exceptions.md#jsonexceptionout_of_range415) if the subtype of a binary value
exceeds 255, the maximum of the BSON binary subtype; example:
`"subtype 70000 is too large for the BSON binary subtype (max 255)"`
- Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key is
not valid UTF-8 and `error_handler` is `strict` (the default only if
[`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled)
## Complexity
@@ -98,3 +110,7 @@ pass before anything is written.
- Throws `out_of_range.412` and `out_of_range.415` since version 3.13.0.
- Linear in the size of `j`, and no longer limited by the call stack for deeply nested values, since version 3.13.0.
- `out_of_range.415` is now detected before anything is written, like the other exceptions above, since version 3.13.0.
- Added `error_handler` parameter in version 3.13.0. Its default, `keep`, writes the bytes of a string or object key
that is not valid UTF-8 unchanged, as before; `strict` (the default if
[`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled) throws `type_error.316` before anything
is written.
docs/mkdocs/docs/api/basic_json/to_cbor.md
+21 -3
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@@ -2,11 +2,14 @@
```cpp
// (1)
static std::vector<std::uint8_t> to_cbor(const basic_json& j);
static std::vector<std::uint8_t> to_cbor(const basic_json& j,
const error_handler_t error_handler = error_handler_t::keep);
// (2)
static void to_cbor(const basic_json& j, detail::output_adapter<std::uint8_t> o);
static void to_cbor(const basic_json& j, detail::output_adapter<char> o);
static void to_cbor(const basic_json& j, detail::output_adapter<std::uint8_t> o,
const error_handler_t error_handler = error_handler_t::keep);
static void to_cbor(const basic_json& j, detail::output_adapter<char> o,
const error_handler_t error_handler = error_handler_t::keep);
```
Serializes a given JSON value `j` to a byte vector using the CBOR (Concise Binary Object Representation) serialization
@@ -26,6 +29,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
`o` (in)
: output adapter to write serialization to
`error_handler` (in)
: how to treat a string or object key in `j` that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
The default, `keep`, writes the ill-formed bytes to the output as is, as every version of `to_cbor` did before
this parameter was added; `strict` throws; `replace`/`ignore` sanitize it the same way [`dump`](dump.md) would.
If [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled, the default is `strict` instead.
## Return value
1. CBOR serialization as a byte vector
@@ -35,6 +44,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
## Exceptions
- Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key in `j` is
not valid UTF-8 and `error_handler` is `strict` (the default only if
[`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled)
## Complexity
Linear in the size of the JSON value `j`.
@@ -68,3 +83,6 @@ Linear in the size of the JSON value `j`.
- Added in version 2.0.9.
- Compact representation of floating-point numbers added in version 3.8.0.
- Added `error_handler` parameter in version 3.13.0. Its default, `keep`, writes the bytes of a string or object key
that is not valid UTF-8 unchanged, as before; `strict` (the default if
[`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled) throws `type_error.316`.
docs/mkdocs/docs/api/basic_json/to_msgpack.md
+17 -3
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@@ -2,11 +2,14 @@
```cpp
// (1)
static std::vector<std::uint8_t> to_msgpack(const basic_json& j);
static std::vector<std::uint8_t> to_msgpack(const basic_json& j,
const error_handler_t error_handler = error_handler_t::keep);
// (2)
static void to_msgpack(const basic_json& j, detail::output_adapter<std::uint8_t> o);
static void to_msgpack(const basic_json& j, detail::output_adapter<char> o);
static void to_msgpack(const basic_json& j, detail::output_adapter<std::uint8_t> o,
const error_handler_t error_handler = error_handler_t::keep);
static void to_msgpack(const basic_json& j, detail::output_adapter<char> o,
const error_handler_t error_handler = error_handler_t::keep);
```
Serializes a given JSON value `j` to a byte vector using the MessagePack serialization format. MessagePack is a binary
@@ -25,6 +28,13 @@ The exact mapping and its limitations are described on a [dedicated page](../../
`o` (in)
: output adapter to write serialization to
`error_handler` (in)
: how to treat a string or object key in `j` that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
The default, `keep`, writes the ill-formed bytes to the output as is, as every version of `to_msgpack` did before
this parameter was added and as the MessagePack specification allows; `strict` throws; `replace`/`ignore` sanitize
it the same way [`dump`](dump.md) would. Unlike the other binary writers, the default stays `keep` even if
[`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled.
## Return value
1. MessagePack serialization as a byte vector
@@ -42,6 +52,8 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
- Throws [`out_of_range.415`](../../home/exceptions.md#jsonexceptionout_of_range415) if the subtype of a binary value
exceeds 255, the maximum of the MessagePack ext type; example:
`"subtype 70000 is too large for the MessagePack ext type (max 255)"`
- Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key in `j` is
not valid UTF-8 and `error_handler` is `strict`
## Complexity
@@ -91,6 +103,8 @@ Linear in the size of the JSON value `j`.
- Added in version 2.0.9.
- Throws `out_of_range.412` and `out_of_range.415` since version 3.13.0.
- Added `error_handler` parameter in version 3.13.0. Its default, `keep`, writes the bytes of a string or object key
that is not valid UTF-8 unchanged, as before.
- Fixed in version 3.13.0 to serialize `number_integer_t`/`number_unsigned_t` pairs of different width correctly;
before, integers could be serialized with the wrong value if `number_integer_t` was narrower than
`number_unsigned_t`.
docs/mkdocs/docs/api/basic_json/to_ubjson.md
+18 -3
View File
@@ -4,13 +4,16 @@
// (1)
static std::vector<std::uint8_t> to_ubjson(const basic_json& j,
const bool use_size = false,
const bool use_type = false);
const bool use_type = false,
const error_handler_t error_handler = error_handler_t::keep);
// (2)
static void to_ubjson(const basic_json& j, detail::output_adapter<std::uint8_t> o,
const bool use_size = false, const bool use_type = false);
const bool use_size = false, const bool use_type = false,
const error_handler_t error_handler = error_handler_t::keep);
static void to_ubjson(const basic_json& j, detail::output_adapter<char> o,
const bool use_size = false, const bool use_type = false);
const bool use_size = false, const bool use_type = false,
const error_handler_t error_handler = error_handler_t::keep);
```
Serializes a given JSON value `j` to a byte vector using the UBJSON (Universal Binary JSON) serialization format. UBJSON
@@ -36,6 +39,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
: whether to add type annotations to container types (must be combined with `#!cpp use_size = true`); optional,
`#!cpp false` by default.
`error_handler` (in)
: how to treat a string or object key in `j` that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
The default, `keep`, writes the ill-formed bytes to the output as is, as every version of `to_ubjson` did before
this parameter was added; `strict` throws; `replace`/`ignore` sanitize it the same way [`dump`](dump.md) would.
If [`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled, the default is `strict` instead.
## Return value
1. UBJSON serialization as a byte vector
@@ -49,6 +58,9 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
- Throws [`other_error.502`](../../home/exceptions.md#jsonexceptionother_error502) if `use_type` is true and `use_size`
is false, and `j` contains a non-empty array, object, or binary value.
- Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key in `j` is
not valid UTF-8 and `error_handler` is `strict` (the default only if
[`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled)
## Complexity
@@ -97,3 +109,6 @@ Linear in the size of the JSON value `j`.
## Version history
- Added in version 3.1.0.
- Added `error_handler` parameter in version 3.13.0. Its default, `keep`, writes the bytes of a string or object key
that is not valid UTF-8 unchanged, as before; `strict` (the default if
[`JSON_STRICT_BINARY_UTF8`](../macros/json_strict_binary_utf8.md) is enabled) throws `type_error.316`.
docs/mkdocs/docs/api/basic_json/value.md
+3 -1
View File
@@ -223,7 +223,9 @@ changes to any JSON value.
1. Added in version 1.0.0. Changed parameter `default_value` type from `const ValueType&` to `ValueType&&` in version
3.11.0. Deleted overload for integral key types added in version 3.13.0 to reject such calls at compile time
instead of causing undefined behavior at runtime.
2. Added in version 3.11.0. Made `ValueType` the first template parameter in version 3.11.2.
2. Added in version 3.11.0. Made `ValueType` the first template parameter in version 3.11.2. Fixed in version 3.13.0
to consistently accept `std::string_view`-convertible keys, as already supported by
[`operator[]`](operator[].md), [`at`](at.md), [`find`](find.md), and other lookup functions.
3. Added in version 2.0.2. Extended to work with arrays in version 3.13.0, including fixing an issue where resolving
`ptr` through an array unexpectedly threw `out_of_range` instead of returning the resolved element (or
`default_value`, as documented).
docs/mkdocs/docs/api/macros/index.md
+2
View File
@@ -18,6 +18,8 @@ header. See also the [macro overview page](../../features/macros.md).
- [**JSON_PRECISE_STREAM_POSITION**](json_precise_stream_position.md) - opt in to leaving an input stream positioned
right after a parsed number
- [**JSON_STRICT_BINARY_UTF8**](json_strict_binary_utf8.md) - opt in to checking strings for valid UTF-8 in the CBOR,
UBJSON, BJData, and BSON writers
- [**JSON_STRICT_NUL_HANDLING**](json_strict_nul_handling.md) - opt in to rejecting a NUL byte in the input instead of
treating it as end of input
docs/mkdocs/docs/api/macros/json_brace_init_copy_semantics.md
+1
View File
@@ -115,3 +115,4 @@ The default value is `0` (disabled — existing behavior is preserved).
## Version history
- Added in version 3.13.0.
- Planned to become the default (with the macro removed) in version 4.0.0.
docs/mkdocs/docs/api/macros/json_no_automatic_udls.md
+2 -1
View File
@@ -43,9 +43,9 @@ By default, `#!cpp JSON_NO_AUTOMATIC_UDLS` is not defined, and `<nlohmann/json.h
```cpp
// compiled with -DJSON_NO_AUTOMATIC_UDLS for the whole project
#include <nlohmann/json.hpp>
// this file uses the literals, so it includes them explicitly
// (the header includes <nlohmann/json.hpp> itself)
#include <nlohmann/json_literals.hpp>
int main()
@@ -62,6 +62,7 @@ By default, `#!cpp JSON_NO_AUTOMATIC_UDLS` is not defined, and `<nlohmann/json.h
- [`operator""_json`](../operator_literal_json.md)
- [`operator""_json_pointer`](../operator_literal_json_pointer.md)
- [`JSON_USE_GLOBAL_UDLS`](json_use_global_udls.md) - place user-defined string literals (UDLs) into the global namespace
- [Compile times](../../integration/compile_times.md) - options to reduce compile times
## Version history
docs/mkdocs/docs/api/macros/json_strict_binary_utf8.md
+101
View File
@@ -0,0 +1,101 @@
# JSON_STRICT_BINARY_UTF8
```cpp
#define JSON_STRICT_BINARY_UTF8 /* value */
```
When defined to `1`, the `error_handler` parameter of the binary writers [`to_cbor`](../basic_json/to_cbor.md),
[`to_ubjson`](../basic_json/to_ubjson.md), [`to_bjdata`](../basic_json/to_bjdata.md), and
[`to_bson`](../basic_json/to_bson.md) defaults to [`error_handler_t::strict`](../basic_json/error_handler_t.md) instead
of `error_handler_t::keep`. These writers then check every string value and object key for valid UTF-8 and throw
[`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) for ill-formed UTF-8, like
[`dump`](../basic_json/dump.md) does. Without it, they write the bytes unchanged. An `error_handler` passed explicitly
always takes precedence.
The macro does not affect:
- [`to_msgpack`](../basic_json/to_msgpack.md): the MessagePack specification allows a `str` value to contain bytes that
are not valid UTF-8, so its `error_handler` always defaults to `keep`.
- [`to_bon8`](../basic_json/to_bon8.md): BON8 always checks, because the UTF-8 lead bytes mark where a string ends.
- The binary readers ([`from_cbor`](../basic_json/from_cbor.md), [`from_msgpack`](../basic_json/from_msgpack.md),
[`from_ubjson`](../basic_json/from_ubjson.md), [`from_bjdata`](../basic_json/from_bjdata.md),
[`from_bson`](../basic_json/from_bson.md)): none of these formats requires a decoder to reject ill-formed UTF-8, so
they always return the bytes unchanged.
## Default definition
The default value is `0` (disabled, the behavior of version 3.12.0 and earlier is preserved).
```cpp
#define JSON_STRICT_BINARY_UTF8 0
```
## Notes
!!! note "Background"
CBOR, UBJSON, BJData, and BSON all require strings to be UTF-8. Up to version 3.12.0, the writers did not check
this, so they could produce output that other decoders reject. Checking by default would break code that stores
other encodings (for instance ISO 8859-1) in a string and only ever writes it to a binary format. You can pass
`error_handler_t::strict` to each call, or use this macro to check by default ahead of version 4.0.0, where
`strict` is planned to become the default (see
[#5529](https://github.com/nlohmann/json/issues/5529) and [#5651](https://github.com/nlohmann/json/issues/5651)).
!!! warning "Opt-in only"
This macro must be defined **before** including `<nlohmann/json.hpp>`. Defining it after the include has no
effect.
!!! note "ABI compatibility"
The value of this macro is encoded in the [namespace](../../features/namespace.md) (tag `_sbu8`), resulting in
distinct symbol names. Translation units compiled with and without it can therefore be linked into the same program
without One Definition Rule (ODR) violations, but they cannot exchange instances of library types.
## Examples
??? example "Example: default behavior (macro not defined)"
Without the macro, the bytes are written unchanged:
```cpp
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
auto v = json::to_cbor(json("\xFF"));
// v is {0x61, 0xFF}
}
```
??? example "Example: opt-in check (macro defined to 1)"
With the macro, ill-formed UTF-8 is rejected:
```cpp
#define JSON_STRICT_BINARY_UTF8 1
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
auto v = json::to_cbor(json("\xFF"));
// throws type_error.316: invalid UTF-8 byte at index 0: 0xFF
}
```
## See also
- [**to_cbor**](../basic_json/to_cbor.md) - create a CBOR serialization of a JSON value
- [**to_ubjson**](../basic_json/to_ubjson.md) - create a UBJSON serialization of a JSON value
- [**to_bjdata**](../basic_json/to_bjdata.md) - create a BJData serialization of a JSON value
- [**to_bson**](../basic_json/to_bson.md) - create a BSON serialization of a JSON value
- [**error_handler_t**](../basic_json/error_handler_t.md) - how [`dump`](../basic_json/dump.md) treats ill-formed UTF-8
## Version history
- Added in version 3.13.0.
- Planned to become the default (with the macro removed) in version 4.0.0.
docs/mkdocs/docs/api/macros/json_use_implicit_conversions.md
+24 -2
View File
@@ -5,7 +5,9 @@
```
When defined to `0`, implicit conversions are switched off. By default, implicit conversions are switched on. The
value directly affects [`operator ValueType`](../basic_json/operator_ValueType.md).
value directly affects [`operator ValueType`](../basic_json/operator_ValueType.md) and the
[converting constructor](../basic_json/basic_json.md) from a `basic_json` specialization with a different string
type (overload 4).
## Default definition
@@ -42,7 +44,7 @@ By default, implicit conversions are enabled.
## Examples
??? example
??? example "Example: implicit conversion"
This is an example for an implicit conversion:
@@ -59,6 +61,25 @@ By default, implicit conversions are enabled.
auto s = j.get<std::string>();
```
??? example "Example: conversion between `basic_json` specializations"
A `basic_json` specialization with a different string type is also no longer converted implicitly when
`JSON_USE_IMPLICIT_CONVERSIONS` is defined to `0`:
```cpp
using wjson = nlohmann::basic_json<std::map, std::vector, std::wstring>;
void load(const nlohmann::json& j);
wjson wj = /* ... */;
load(wj); // error: no implicit conversion
load(nlohmann::json(wj)); // OK: explicit conversion
load(wj.get<nlohmann::json>()); // OK: explicit conversion
```
Specializations that share the same string type, such as `json` and `ordered_json`, remain implicitly
convertible.
## See also
- [**operator ValueType**](../basic_json/operator_ValueType.md) - get a value (implicit)
@@ -68,3 +89,4 @@ By default, implicit conversions are enabled.
## Version history
- Added in version 3.9.0.
- Also affects the conversion between `basic_json` specializations with different string types since version 3.13.0.
docs/mkdocs/docs/api/macros/json_use_legacy_discarded_value_comparison.md
+3
View File
@@ -81,3 +81,6 @@ When the macro is not defined, the library will define it to its default value.
## Version history
- Added in version 3.11.0.
- Fixed in version 3.13.0 so `<=` and `>=` also emulate the legacy behavior in C++20 when the JSON value is the
right-hand operand of a scalar comparison; before, only the 3-way-comparison-rewritten candidate was found, which
yielded `#!cpp false` instead of `#!cpp true`.
docs/mkdocs/docs/community/roadmap.md
+65 -5
View File
@@ -14,7 +14,7 @@ work items are tracked in the [GitHub milestones](https://github.com/nlohmann/js
opt-in.
- **Keep the 3.x public API stable.** Releases follow [semantic versioning](https://semver.org). Changes that would
break existing code are only added behind a feature macro, so users can opt in and test their code before a next
major release.
major release, see [Version 4.0](#version-40).
- **Support a broad range of compilers and platforms.** The [CI](quality_assurance.md) keeps testing old and new
versions of GCC, Clang, MSVC, and other compilers on Linux, macOS, and Windows.
- **Keep the quality assurance up.** Every change keeps the test coverage at 100%, passes the static and dynamic
@@ -37,7 +37,67 @@ work items are tracked in the [GitHub milestones](https://github.com/nlohmann/js
## Version 4.0
There is no decision yet on whether or when a version 4.0 with breaking changes will be released. Proposals that need
a major version, for instance stricter type conversions, are collected in issue
[#3453](https://github.com/nlohmann/json/issues/3453). Until then, such changes are only added as opt-in behavior
behind feature macros.
There is no release date for version 4.0 yet. Proposals that need a major version, for instance stricter type
conversions, are collected in issue [#3453](https://github.com/nlohmann/json/issues/3453).
!!! note "Not final"
The plan for version 4.0 described below is not final and may still change: macros may be added to or removed from
the list, and planned defaults may be revised. Any such change will be documented on this page.
### Trying out 4.0 today
Version 4.0 will not be developed on a separate branch. Instead, every breaking change is first added to a 3.x release
behind a macro whose default keeps the 3.x behavior. Version 4.0 then switches the defaults and removes the macros.
Version 4.0 is therefore the sum of these macros: you can try it on the 3.x release train today by defining each macro
to its 4.0 value and fixing what no longer compiles or behaves differently. Once your code works with all of them, it
is ready for version 4.0.
The following macros guard changes that are planned to become the default in version 4.0:
| Macro | 3.x default | 4.0 behavior | CMake option | Added |
|------------------------------------------------------------------------------------------------------------------|-------------|-------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------|--------|
| [`JSON_USE_IMPLICIT_CONVERSIONS`](../api/macros/json_use_implicit_conversions.md) | `1` | `0`: no implicit conversions from `basic_json` to other types; use [`get`](../api/basic_json/get.md) instead | [`JSON_ImplicitConversions`](../integration/cmake.md#json_implicitconversions) | 3.9.0 |
| [`JSON_USE_GLOBAL_UDLS`](../api/macros/json_use_global_udls.md) | `1` | `0`: the string literals `_json` and `_json_pointer` are only available in namespace `nlohmann::literals` | [`JSON_GlobalUDLs`](../integration/cmake.md#json_globaludls) | 3.11.0 |
| [`JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON`](../api/macros/json_use_legacy_discarded_value_comparison.md) | `0` | removed: the deprecated legacy comparison of discarded values can no longer be enabled | [`JSON_LegacyDiscardedValueComparison`](../integration/cmake.md#json_legacydiscardedvaluecomparison) | 3.11.0 |
| [`JSON_BRACE_INIT_COPY_SEMANTICS`](../api/macros/json_brace_init_copy_semantics.md) | `0` | `1`: single-element brace initialization such as `#!cpp json j{obj};` copies the element instead of creating an array | – | 3.13.0 |
| [`JSON_PRECISE_STREAM_POSITION`](../api/macros/json_precise_stream_position.md) | `0` | `1`: reading from a stream does not consume the character after a number | – | 3.13.0 |
| [`JSON_STRICT_NUL_HANDLING`](../api/macros/json_strict_nul_handling.md) | `0` | `1`: a NUL byte in the input is a parse error instead of the end of input | [`JSON_StrictNulHandling`](../integration/cmake.md#json_strictnulhandling) | 3.13.0 |
| [`JSON_STRICT_BINARY_UTF8`](../api/macros/json_strict_binary_utf8.md) | `0` | `1`: `to_cbor`, `to_ubjson`, `to_bjdata`, and `to_bson` throw for strings that are not valid UTF-8 by default | [`JSON_StrictBinaryUTF8`](../integration/cmake.md#json_strictbinaryutf8) | 3.13.0 |
For example, the following makes a 3.x release behave like version 4.0 with respect to these changes:
```cpp
#define JSON_USE_IMPLICIT_CONVERSIONS 0
#define JSON_USE_GLOBAL_UDLS 0
#define JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON 0
#define JSON_BRACE_INIT_COPY_SEMANTICS 1
#define JSON_PRECISE_STREAM_POSITION 1
#define JSON_STRICT_NUL_HANDLING 1
#define JSON_STRICT_BINARY_UTF8 1
#include <nlohmann/json.hpp>
```
The macros must be defined before the library header is included; setting them once in the build system is the easiest
way to achieve this.
### Removal of deprecated functions
Version 4.0 will remove all deprecated functions. Compiling with deprecation warnings enabled shows which of them your
code still uses. The [migration guide](../integration/migration_guide.md#replace-deprecated-functions) shows how to
replace each of them.
| Deprecated | Since | Migration |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------|----------------------------------------------------------------------------------|
| `#!cpp operator<<(basic_json&, std::istream&)` | 3.0.0 | [Parsing](../integration/migration_guide.md#parsing) |
| `#!cpp operator>>(const basic_json&, std::ostream&)` | 3.0.0 | [Miscellaneous functions](../integration/migration_guide.md#miscellaneous-functions) |
| `iterator_wrapper` | 3.1.0 | [Miscellaneous functions](../integration/migration_guide.md#miscellaneous-functions) |
| [`parse`](../api/basic_json/parse.md), [`accept`](../api/basic_json/accept.md), and [`sax_parse`](../api/basic_json/sax_parse.md) with an initializer list `{ptr, len}` or `{first, last}` | 3.8.0 | [Parsing](../integration/migration_guide.md#parsing) |
| [`from_bson`](../api/basic_json/from_bson.md), [`from_cbor`](../api/basic_json/from_cbor.md), [`from_msgpack`](../api/basic_json/from_msgpack.md), and [`from_ubjson`](../api/basic_json/from_ubjson.md) with `(ptr, len)` or an initializer list | 3.8.0 | [Parsing](../integration/migration_guide.md#parsing) |
| [`json_pointer::operator string_t`](../api/json_pointer/operator_string_t.md) | 3.11.0 | [JSON Pointers](../integration/migration_guide.md#json-pointers) |
| [`json_pointer`](../api/json_pointer/index.md) with a `basic_json` type as template argument, and the overloads of `value`, `contains`, `operator[]`, and `at` accepting such a pointer | 3.11.0 | [JSON Pointers](../integration/migration_guide.md#json-pointers) |
| Comparing a [`json_pointer`](../api/json_pointer/index.md) with a string via [`operator==`](../api/json_pointer/operator_eq.md) or [`operator!=`](../api/json_pointer/operator_ne.md) | 3.11.2 | [JSON Pointers](../integration/migration_guide.md#json-pointers) |
The deprecated legacy comparison of discarded values is controlled by a macro and therefore listed in the table above.
New breaking changes will follow the same path: they are added to these tables when they land in a 3.x release.
docs/mkdocs/docs/examples/as_base_class.cpp
+41
View File
@@ -0,0 +1,41 @@
#include <iostream>
#include <nlohmann/json.hpp>
class base_class_with_hidden_members
{
public:
const char* type_name() const noexcept
{
return "my_type_name";
}
std::size_t size() const noexcept
{
return 42;
}
};
using json = nlohmann::basic_json <
std::map,
std::vector,
std::string,
bool,
std::int64_t,
std::uint64_t,
double,
std::allocator,
nlohmann::adl_serializer,
std::vector<std::uint8_t>,
base_class_with_hidden_members
>;
int main()
{
json j = {1, 2, 3};
// the members of basic_json hide the members of the base class
std::cout << j.type_name() << ' ' << j.size() << '\n';
// access the hidden members of the base class
std::cout << j.as_base_class().type_name() << ' ' << j.as_base_class().size() << '\n';
}
docs/mkdocs/docs/examples/as_base_class.output
+2
View File
@@ -0,0 +1,2 @@
array 3
my_type_name 42
docs/mkdocs/docs/examples/error_handler_t.cpp
+2 -1
View File
@@ -20,5 +20,6 @@ int main()
<< j_invalid.dump(-1, ' ', false, json::error_handler_t::replace)
<< "\nstring with ignored invalid characters: "
<< j_invalid.dump(-1, ' ', false, json::error_handler_t::ignore)
<< '\n';
<< "\nstring with the invalid byte kept as is (" << j_invalid.dump(-1, ' ', false, json::error_handler_t::keep).size()
<< " bytes, not valid UTF-8 itself)\n";
}
docs/mkdocs/docs/examples/error_handler_t.output
+1
View File
@@ -1,3 +1,4 @@
[json.exception.type_error.316] invalid UTF-8 byte at index 2: 0xA9
string with replaced invalid characters: "ä�ü"
string with ignored invalid characters: "äü"
string with the invalid byte kept as is (7 bytes, not valid UTF-8 itself)
docs/mkdocs/docs/features/arbitrary_types.md
+1
View File
@@ -79,6 +79,7 @@ Some important things:
* When using `get<your_type>()`, `your_type` **MUST** be [DefaultConstructible](https://en.cppreference.com/w/cpp/named_req/DefaultConstructible). (There is a way to bypass this requirement described later.)
* In function `from_json`, use function [`at()`](../api/basic_json/at.md) to access the object values rather than `operator[]`. In case a key does not exist, `at` throws an exception that you can handle, whereas `operator[]` exhibits undefined behavior.
* You do not need to add serializers or deserializers for STL types like `std::vector`: the library already implements these.
* If you control the type, consider defining `to_json`/`from_json` as `friend` functions inside the class ("hidden friends"). Argument-dependent lookup then only finds them for your type, which also avoids a [GCC < 11 compilation error](../home/faq.md#incomplete-detector-type-with-gcc-11).
??? example "Example: serialize a `person` to JSON with `to_json`"
docs/mkdocs/docs/features/assertions.md
+31 -7
View File
@@ -16,14 +16,15 @@ before including the `json.hpp` header.
## Function with runtime assertions
### Unchecked object access to a const value
### Unchecked access to a const value
Function [`operator[]`](../api/basic_json/operator%5B%5D.md) implements unchecked access for objects. Whereas a missing
key is added in the case of non-const objects, accessing a const object with a missing key is undefined behavior (think
of a dereferenced null pointer) and yields a runtime assertion.
Function [`operator[]`](../api/basic_json/operator%5B%5D.md) implements unchecked access for arrays and objects. Whereas
a missing element is added in the case of non-const values, accessing a const value with a missing object key or an
invalid array index is undefined behavior (think of a dereferenced null pointer) and yields a runtime assertion. This
also applies to a [JSON pointer](json_pointer.md) that refers to a missing key or an invalid index.
If you are not sure whether an element in an object exists, use checked access with the
[`at` function](../api/basic_json/at.md) or call the [`contains` function](../api/basic_json/contains.md) before.
If you are not sure whether an element exists, use checked access with the [`at` function](../api/basic_json/at.md)
or call the [`contains` function](../api/basic_json/contains.md) before.
See also the documentation on [element access](element_access/index.md).
@@ -46,7 +47,30 @@ See also the documentation on [element access](element_access/index.md).
Output:
```
Assertion failed: (m_value.object->find(key) != m_value.object->end()), function operator[], file json.hpp, line 2144.
Assertion failed: (it != m_data.m_value.object->end()), function operator[], file json.hpp, line 28795.
```
??? example "Example 2: Invalid array index in a JSON pointer"
The following code will trigger an assertion at runtime:
```cpp
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
int main()
{
const json j = {{"array", {1, 2, 3}}};
auto v = j["/array/5"_json_pointer];
}
```
Output:
```
Assertion failed: (idx < m_data.m_value.array->size()), function operator[], file json.hpp, line 28758.
```
### Constructing from an uninitialized iterator range
docs/mkdocs/docs/features/binary_formats/bjdata.md
+22
View File
@@ -63,6 +63,15 @@ The library uses the following mapping from JSON values types to BJData types ac
- strings with more than 18446744073709551615 bytes, i.e., 2<sup>64</sup>-1 bytes (theoretical)
!!! warning "UTF-8 validation of string values and object keys"
BJData strings must use UTF-8 encoding. By default (the [`error_handler`](../../api/basic_json/to_bjdata.md)
parameter left at `keep`), `to_bjdata()` writes the bytes of string values and object keys unchanged, even if they
are not valid UTF-8. With `error_handler_t::strict`, it throws
[`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) for ill-formed UTF-8 instead;
`replace`/`ignore` sanitize the string. [`JSON_STRICT_BINARY_UTF8`](../../api/macros/json_strict_binary_utf8.md)
makes `strict` the default.
!!! info "Unused BJData markers"
The following markers are not used in the conversion:
@@ -208,6 +217,19 @@ The library maps BJData types to JSON value types as follows:
The mapping is **complete** in the sense that any BJData value can be converted to a JSON value.
!!! warning "Ill-formed UTF-8 in string values and object keys"
BJData strings must use UTF-8 encoding, but checking it on read is opt-in: with the
[`error_handler`](../../api/basic_json/from_bjdata.md) parameter left at `keep` (the default), `from_bjdata()`
accepts a string value or object key whose bytes are not valid UTF-8 and hands them back unchanged. Passing
`error_handler_t::strict` makes `from_bjdata()` check and throw
[`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) for ill-formed UTF-8, and
`replace`/`ignore` sanitize the string instead of keeping it. However,
[`dump()`](../../api/basic_json/dump.md) still requires valid UTF-8 and throws
[`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) for a value read with the default
`keep` handler, unless an error handler is passed that replaces or ignores the ill-formed bytes. `to_bjdata()`'s
own `error_handler` parameter defaults to `keep` (see above), so such a value is written back unchanged.
!!! info "Round trips"
A value returned by [`from_bjdata`](../../api/basic_json/from_bjdata.md) can be serialized with
docs/mkdocs/docs/features/binary_formats/bson.md
+14 -7
View File
@@ -109,14 +109,21 @@ The library maps BSON record types to JSON value types as follows:
If BSON input must be validated for strict specification compliance, validate it separately before passing it to
`from_bson()`.
!!! warning "UTF-8 validation of string values"
!!! warning "Ill-formed UTF-8 in string values"
The BSON specification requires `string` values (type `0x02`) to be valid UTF-8. This library validates the
bytes of every such string at decode time and rejects ill-formed UTF-8 with a
[`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) exception (or, with `allow_exceptions`
set to `false`, a discarded value), rather than only failing later when the resulting value is dumped. Element
(key) names and `binary` values (type `0x05`) are unaffected and are never validated, since they are read
byte-by-byte as a C string, or are not required to hold text, respectively.
The BSON specification requires `string` values (type `0x02`) to be valid UTF-8, but this is not required of a
decoder, so checking is opt-in: with the [`error_handler`](../../api/basic_json/from_bson.md) parameter left at
`keep` (the default), `from_bson()` accepts a `string` value whose bytes are not valid UTF-8 and hands them back
unchanged. Passing `error_handler_t::strict` makes `from_bson()` check and throw
[`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) for ill-formed UTF-8, and
`replace`/`ignore` sanitize the string instead of keeping it. However, [`dump()`](../../api/basic_json/dump.md)
still requires valid UTF-8 and throws [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) for a
value read with the default `keep` handler, unless an error handler is passed that replaces or ignores the
ill-formed bytes. `to_bson()`'s own `error_handler` parameter defaults to `keep`, so such a string value or element
(key) name is written unchanged; with `strict` (the default if
[`JSON_STRICT_BINARY_UTF8`](../../api/macros/json_strict_binary_utf8.md) is enabled), it throws the same exception
instead. Element (key) names are never validated on read, since they are read byte-by-byte as a C string. `binary`
values (type `0x05`) are unaffected, since they are not required to hold text.
??? example "Example: deserialize a JSON value from BSON"
docs/mkdocs/docs/features/binary_formats/cbor.md
+14 -8
View File
@@ -189,15 +189,21 @@ The library maps CBOR types to JSON value types as follows:
([RFC 8392](https://www.rfc-editor.org/rfc/rfc8392.html)), cannot be read with this library and need a
general-purpose CBOR library instead.
!!! warning "UTF-8 validation of text strings"
!!! warning "Ill-formed UTF-8 in text strings"
[RFC 8949, Section 3.1](https://www.rfc-editor.org/rfc/rfc8949.html#section-3.1) requires CBOR text strings
(major type 3) to be valid UTF-8. This library validates the bytes of every text string (object keys included) at
decode time and rejects ill-formed UTF-8 with a
[`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) exception (or, with
`allow_exceptions` set to `false`, a discarded value), rather than only failing later when the resulting value is
dumped. Byte strings (major type 2) are unaffected and are never validated, since they are not required to hold
text.
[RFC 8949, Section 3.1](https://www.rfc-editor.org/rfc/rfc8949.html#section-3.1) requires CBOR text strings (major
type 3) to be valid UTF-8, but leaves it up to the decoder whether to enforce this, so checking is opt-in: with the
[`error_handler`](../../api/basic_json/from_cbor.md) parameter left at `keep` (the default), `from_cbor()` accepts a
text string (object keys included) whose bytes are not valid UTF-8 and hands them back unchanged. Passing
`error_handler_t::strict` makes `from_cbor()` check and throw
[`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) for ill-formed UTF-8, and
`replace`/`ignore` sanitize the string instead of keeping it. However, [`dump()`](../../api/basic_json/dump.md)
still requires valid UTF-8 and throws [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) for a
value read with the default `keep` handler, unless an error handler is passed that replaces or ignores the
ill-formed bytes. `to_cbor()`'s own [`error_handler`](../../api/basic_json/to_cbor.md) parameter defaults to `keep`,
so such a value is written back unchanged; with `strict` (the default if
[`JSON_STRICT_BINARY_UTF8`](../../api/macros/json_strict_binary_utf8.md) is enabled), it throws the same exception
instead. Byte strings (major type 2) are unaffected, since they are not required to hold text.
!!! warning "Tagged items"
docs/mkdocs/docs/features/binary_formats/messagepack.md
+16 -7
View File
@@ -153,14 +153,23 @@ The library maps MessagePack types to JSON value types as follows:
This applies to the [SAX interface](../parsing/sax_interface.md) as well, as the key is read before it is passed
on. Such input needs a general-purpose MessagePack library instead.
!!! warning "UTF-8 validation of string values"
!!! warning "Ill-formed UTF-8 in string values"
The MessagePack specification requires `str` values (`fixstr`, `str 8`, `str 16`, `str 32`) to be valid UTF-8.
This library validates the bytes of every such string (object keys included) at decode time and rejects
ill-formed UTF-8 with a [`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) exception (or,
with `allow_exceptions` set to `false`, a discarded value), rather than only failing later when the resulting
value is dumped. `bin`/`ext`/`fixext` values are unaffected and are never validated, since they are not required
to hold text.
The MessagePack specification explicitly allows a `str` value (`fixstr`, `str 8`, `str 16`, `str 32`) to contain
a byte sequence that is not valid UTF-8, and expects a deserializer to hand the original bytes back unchanged.
This library follows that by default: with its
[`error_handler`](../../api/basic_json/from_msgpack.md) parameter left at `keep` (the default),
`from_msgpack()` reads `str` bytes (object keys included) as-is, without validating them, so such a value
round-trips through `from_msgpack(to_msgpack(j))` byte for byte. Passing `error_handler_t::strict` makes
`from_msgpack()` check anyway and throw
[`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) for ill-formed UTF-8, and
`replace`/`ignore` sanitize the string instead of keeping it. `to_msgpack()` also writes `str` bytes as-is by
default, since the specification permits it; its [`error_handler`](../../api/basic_json/to_msgpack.md) parameter
can be set to `strict` to throw [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) instead, or
to `replace`/`ignore` to sanitize the string, for instance for a decoder that rejects ill-formed UTF-8. However,
[`dump()`](../../api/basic_json/dump.md) still requires valid UTF-8 and throws
[`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) for a value read this way with the
default `keep` handler, unless an error handler is passed that replaces or ignores the ill-formed bytes.
??? example "Example: deserialize a JSON value from MessagePack"
docs/mkdocs/docs/features/binary_formats/ubjson.md
+22
View File
@@ -47,6 +47,15 @@ The library uses the following mapping from JSON values types to UBJSON types ac
- strings with more than 9223372036854775807 bytes (theoretical)
!!! warning "UTF-8 validation of string values and object keys"
UBJSON's required string encoding is UTF-8. By default (the [`error_handler`](../../api/basic_json/to_ubjson.md)
parameter left at `keep`), `to_ubjson()` writes the bytes of string values and object keys unchanged, even if they
are not valid UTF-8. With `error_handler_t::strict`, it throws
[`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) for ill-formed UTF-8 instead;
`replace`/`ignore` sanitize the string. [`JSON_STRICT_BINARY_UTF8`](../../api/macros/json_strict_binary_utf8.md)
makes `strict` the default.
!!! info "Unused UBJSON markers"
The following markers are not used in the conversion:
@@ -120,6 +129,19 @@ The library maps UBJSON types to JSON value types as follows:
The mapping is **complete** in the sense that any UBJSON value can be converted to a JSON value.
!!! warning "Ill-formed UTF-8 in string values and object keys"
UBJSON's required string encoding is UTF-8, but checking it on read is opt-in: with the
[`error_handler`](../../api/basic_json/from_ubjson.md) parameter left at `keep` (the default), `from_ubjson()`
accepts a string value or object key whose bytes are not valid UTF-8 and hands them back unchanged. Passing
`error_handler_t::strict` makes `from_ubjson()` check and throw
[`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) for ill-formed UTF-8, and
`replace`/`ignore` sanitize the string instead of keeping it. However,
[`dump()`](../../api/basic_json/dump.md) still requires valid UTF-8 and throws
[`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) for a value read with the default
`keep` handler, unless an error handler is passed that replaces or ignores the ill-formed bytes. `to_ubjson()`'s
own `error_handler` parameter defaults to `keep` (see above), so such a value is written back unchanged.
??? example "Example: deserialize a JSON value from UBJSON"
```cpp
docs/mkdocs/docs/features/macros.md
+14
View File
@@ -138,6 +138,20 @@ using the library with compilers that do not fully support C++11 and may only wo
See [full documentation of `JSON_SKIP_UNSUPPORTED_COMPILER_CHECK`](../api/macros/json_skip_unsupported_compiler_check.md).
## `JSON_STRICT_BINARY_UTF8`
When defined to `1`, [`to_cbor`](../api/basic_json/to_cbor.md), [`to_ubjson`](../api/basic_json/to_ubjson.md),
[`to_bjdata`](../api/basic_json/to_bjdata.md), and [`to_bson`](../api/basic_json/to_bson.md) throw
[`type_error.316`](../home/exceptions.md#jsonexceptiontype_error316) for a string value or object key that is not
valid UTF-8. The default value is `0`, which writes the bytes unchanged as before version 3.13.0; this is planned to
become the default in version 4.0.0.
The check can also be enabled with the CMake option
[`JSON_StrictBinaryUTF8`](../integration/cmake.md#json_strictbinaryutf8) (`OFF` by default) which sets
`JSON_STRICT_BINARY_UTF8` accordingly.
See [full documentation of `JSON_STRICT_BINARY_UTF8`](../api/macros/json_strict_binary_utf8.md).
## `JSON_STRICT_NUL_HANDLING`
When defined to `1`, a `'\0'` (NUL) byte anywhere in the input is rejected with `parse_error.101`, like any other
docs/mkdocs/docs/features/namespace.md
+1
View File
@@ -20,6 +20,7 @@ The complete default namespace name is derived as follows:
`_bics`.
- [`JSON_PRECISE_STREAM_POSITION`](../api/macros/json_precise_stream_position.md) defined non-zero appends `_psp`.
- [`JSON_STRICT_NUL_HANDLING`](../api/macros/json_strict_nul_handling.md) defined non-zero appends `_snul`.
- [`JSON_STRICT_BINARY_UTF8`](../api/macros/json_strict_binary_utf8.md) defined non-zero appends `_sbu8`.
- The inline namespace ends with the suffix `_v` followed by the 3 components of the version number separated by
underscores. To omit the version component, see [Disabling the version component](#disabling-the-version-component)
below.
docs/mkdocs/docs/home/exceptions.md
+10 -1
View File
@@ -341,7 +341,10 @@ An unexpected byte was read in a [binary format](../features/binary_formats/inde
A string could not be read from a [binary format](../features/binary_formats/index.md): either a value that is not a
string was read where one was required (for instance as a map key), the string's length specification is invalid, or
the string's bytes are not valid UTF-8.
the string's bytes are not valid UTF-8 and the `error_handler` parameter of the corresponding `from_*` function is
set to `strict`. By default (`error_handler_t::keep`), the bytes of a string are not checked for valid UTF-8 on read;
see the ill-formed UTF-8 notes on the individual [binary format](../features/binary_formats/index.md) pages for how
such a string is handled depending on `error_handler`.
CBOR and MessagePack allow map keys of any type, but JSON object keys are always strings. Maps with keys of any other
type (for instance integers or `null`) are therefore not supported; see the notes on
@@ -749,6 +752,12 @@ The [`unflatten()`](../api/basic_json/unflatten.md) function only works for an o
The [`dump()`](../api/basic_json/dump.md) function only works with UTF-8 encoded strings; that is, if you assign a `std::string` to a JSON value, make sure it is UTF-8 encoded. See the FAQ entry on [serializing untrusted or invalid UTF-8](faq.md#serializing-untrusted-or-invalid-utf-8) for background and the recommended fix.
The binary writers [`to_cbor()`](../api/basic_json/to_cbor.md), [`to_ubjson()`](../api/basic_json/to_ubjson.md),
[`to_bjdata()`](../api/basic_json/to_bjdata.md), and [`to_bson()`](../api/basic_json/to_bson.md) throw this exception
as well for a string value or object key that is not valid UTF-8 if their `error_handler` is `strict` (the default if
[`JSON_STRICT_BINARY_UTF8`](../api/macros/json_strict_binary_utf8.md) is enabled). So does
[`to_msgpack()`](../api/basic_json/to_msgpack.md) if `error_handler_t::strict` is passed.
!!! failure "Example message"
Calling `dump()` on a JSON value containing an ISO 8859-1 encoded string:
docs/mkdocs/docs/home/faq.md
+45
View File
@@ -305,6 +305,51 @@ Only very old NDKs (before r18), which defaulted to GCC and `gnustl`, lacked C++
`std::to_string`. If you run into this, update to a current NDK.
### Incomplete `detector` type with GCC < 11
!!! question
Why does GCC 10 or older fail with `invalid use of incomplete type 'struct nlohmann::detail::detector<..., to_json_function, ...>'` for a type that holds an `optional` member?
This happens with GCC 10 and older in C++11/C++14 mode when all of these hold:
- a class `Holder` has an `optional<Dummy>` member (e.g., `boost::optional`),
- `Dummy` has a constructor taking a `json` value, and
- `to_json` for `Holder` is a free function in the namespace of `Dummy`.
```cpp
class Dummy {
public:
explicit Dummy(const nlohmann::json& j);
};
class Holder {
boost::optional<Dummy> d;
};
void to_json(nlohmann::json& j, const Holder& h); // triggers the error
```
To decide whether `Dummy` is copyable, the compiler checks whether a `Dummy` can be converted to `json`. That check
looks up `to_json` via argument-dependent lookup, finds the unrelated `to_json` for `Holder`, and eventually asks again
whether `Dummy` is copyable. GCC before version 11 turns this cycle into a hard error; GCC 11 and later, Clang, and
C++17 mode compile the code. The same error shows up without this library whenever a constrained converting constructor
is involved, so the library can't avoid it.
To work around this, define `to_json` (and `from_json`) as a *hidden friend* inside the class. That way,
argument-dependent lookup only finds it for `Holder`:
```cpp
class Holder {
boost::optional<Dummy> d;
friend void to_json(nlohmann::json& j, const Holder& h) { /* ... */ }
};
```
The [`NLOHMANN_DEFINE_TYPE_INTRUSIVE`](../api/macros/nlohmann_define_type_intrusive.md) macros define hidden friends as
well. See [#3669](https://github.com/nlohmann/json/issues/3669) for details.
### Missing STL function
!!! question "Questions"
docs/mkdocs/docs/integration/cmake.md
+5
View File
@@ -212,6 +212,11 @@ Use the non-amalgamated version of the library. This option is `ON` by default.
Treat the library headers like system headers (i.e., adding `SYSTEM` to the [`target_include_directories`](https://cmake.org/cmake/help/latest/command/target_include_directories.html) call) to check for this library by tools like Clang-Tidy. This option is `OFF` by default.
### `JSON_StrictBinaryUTF8`
Check string values and object keys for valid UTF-8 in the CBOR, UBJSON, BJData, and BSON writers, by defining the
macro [`JSON_STRICT_BINARY_UTF8`](../api/macros/json_strict_binary_utf8.md). This option is `OFF` by default.
### `JSON_StrictNulHandling`
Reject a `'\0'` (NUL) byte in the input instead of treating it as end of input, by defining the macro
docs/mkdocs/docs/integration/compile_times.md
+149
View File
@@ -0,0 +1,149 @@
# Compile times
The library is header-only and makes heavy use of templates, so every translation unit that includes
`<nlohmann/json.hpp>` pays for parsing the header and instantiating what it uses. This page lists the options to reduce
that cost, ordered by how much they typically save.
!!! info "Measurements"
The numbers below are medians of nine runs compiling a single translation unit with `-std=c++17 -c` against the
single-header version, with Apple clang and GCC 16 on macOS (Apple silicon). They show the order of magnitude to
expect; measure your own code before and after a change.
## Include `json_fwd.hpp` in headers
Header files that only need to *name* the `json` type — for function declarations, members held by pointer or
reference, or friend declarations — can include `<nlohmann/json_fwd.hpp>` instead of `<nlohmann/json.hpp>`. It only
forward-declares `basic_json`, `json`, `ordered_json`, `json_pointer`, and `adl_serializer`. The translation units that
actually use the values then include `<nlohmann/json.hpp>`.
```cpp title="person.hpp"
#pragma once
#include <nlohmann/json_fwd.hpp>
struct person;
void to_json(nlohmann::json& j, const person& p);
void from_json(const nlohmann::json& j, person& p);
```
```cpp title="person.cpp"
#include "person.hpp"
#include <nlohmann/json.hpp>
void to_json(nlohmann::json& j, const person& p) { /* ... */ }
void from_json(const nlohmann::json& j, person& p) { /* ... */ }
```
| Compiler | `json.hpp` (`-O0`) | `json_fwd.hpp` (`-O0`) | Change |
|-------------|-------------------:|-----------------------:|-------:|
| Apple clang | 704 ms | 329 ms | −53% |
| GCC 16 | 779 ms | 242 ms | −69% |
This is the most effective option, because it avoids the full header in every translation unit that includes
*your* headers.
## Opt out of the automatic user-defined string literals
The user-defined string literals [`operator""_json`](../api/operator_literal_json.md) and
[`operator""_json_pointer`](../api/operator_literal_json_pointer.md) are ordinary inline functions whose bodies call the
parser. As `<nlohmann/json.hpp>` includes them by default, every translation unit instantiates the parser, even if it
never parses anything itself.
Define [`JSON_NO_AUTOMATIC_UDLS`](../api/macros/json_no_automatic_udls.md) for the whole project and include
`<nlohmann/json_literals.hpp>` instead of `<nlohmann/json.hpp>` in the files that use the literals (it includes
`<nlohmann/json.hpp>` itself):
```cmake
target_compile_definitions(my_target PRIVATE JSON_NO_AUTOMATIC_UDLS)
```
```cpp
#include <nlohmann/json_literals.hpp> // only where "..."_json is used; includes <nlohmann/json.hpp>
```
The saving applies to translation units that do not parse JSON, for example ones that define types and their
conversions or only pass `json` values around:
| Compiler | Translation unit | Default (`-O0` / `-O2`) | `JSON_NO_AUTOMATIC_UDLS` (`-O0` / `-O2`) | Change |
|-------------|------------------|------------------------:|-----------------------------------------:|------------:|
| Apple clang | model | 776 ms / 846 ms | 629 ms / 692 ms | −19% / −18% |
| GCC 16 | model | 1022 ms / 1120 ms | 882 ms / 965 ms | −14% / −14% |
| Apple clang | parsing | 992 ms / 1815 ms | 1006 ms / 1823 ms | +1% / 0% |
| GCC 16 | parsing | 2018 ms / 3420 ms | 1990 ms / 3454 ms | −1% / +1% |
Translation units that include only the header save up to a third. Translation units that parse anyway instantiate
the parser regardless and see no difference.
## Instantiate `basic_json` once
Each translation unit instantiates the member functions of `nlohmann::json` it uses. An explicit instantiation
declaration tells the compiler that the non-template members are instantiated elsewhere, so it can skip them:
```cpp title="json_instance.hpp"
#pragma once
#include <nlohmann/json.hpp>
extern template class nlohmann::basic_json<>;
```
```cpp title="json_instance.cpp"
#include "json_instance.hpp"
template class nlohmann::basic_json<>;
```
Include `json_instance.hpp` instead of `<nlohmann/json.hpp>` and compile and link `json_instance.cpp` once.
| Compiler | Translation unit | Default (`-O0` / `-O2`) | `extern template` (`-O0` / `-O2`) | Change |
|-------------|---------------------|------------------------:|----------------------------------:|------------:|
| Apple clang | parsing | 992 ms / 1815 ms | 953 ms / 1625 ms | −4% / −10% |
| GCC 16 | parsing | 2018 ms / 3420 ms | 1522 ms / 2728 ms | −25% / −20% |
| Apple clang | `json_instance.cpp` | — | 2166 ms / 4660 ms | — |
| GCC 16 | `json_instance.cpp` | — | 5085 ms / 10616 ms | — |
Notes:
- The saving grows with the number of translation units that use `json`, while the instantiation translation unit is
compiled only once (and is rarely recompiled, as it does not depend on your code).
- Member function templates (such as `get<T>()`, `parse(InputType&&)`, or `value(key, default)`) are not covered by
the explicit instantiation and are still instantiated where they are used.
- The declaration covers exactly `nlohmann::json`. Add the same lines for `nlohmann::ordered_json`
(`nlohmann::basic_json<nlohmann::ordered_map>`) or your own `basic_json` specializations if you use them.
## Use C++20 modules
With a toolchain that supports named modules, `import nlohmann.json;` compiles the library once into a module and
avoids parsing the header in every translation unit. See [Modules](../features/modules.md) for requirements and known
issues. Module support is experimental and currently depends heavily on the compiler version.
## Use precompiled headers
Build systems can precompile `<nlohmann/json.hpp>` together with other stable headers, for example with CMake's
[`target_precompile_headers`](https://cmake.org/cmake/help/latest/command/target_precompile_headers.html):
```cmake
target_precompile_headers(my_target PRIVATE <nlohmann/json.hpp>)
```
This removes the cost of parsing the header, but not of instantiating templates in each translation unit, so it
combines well with the options above.
## Options without effect on compile times
Some configuration macros change what the library declares, but do not measurably change compile times:
| Macro | Apple clang, model (`-O0` / `-O2`) | GCC 16, model (`-O0` / `-O2`) |
|------------------------------------------------------------------------|-----------------------------------:|------------------------------:|
| default | 776 ms / 846 ms | 1022 ms / 1120 ms |
| [`JSON_NO_IO`](../api/macros/json_no_io.md) | 764 ms / 836 ms | 1022 ms / 1117 ms |
| [`JSON_USE_GLOBAL_UDLS`](../api/macros/json_use_global_udls.md)`=0` | 763 ms / 852 ms | 1019 ms / 1106 ms |
`JSON_USE_GLOBAL_UDLS` only controls *where* the literals are declared; to avoid their cost, use
`JSON_NO_AUTOMATIC_UDLS` instead.
## See also
- [`JSON_NO_AUTOMATIC_UDLS`](../api/macros/json_no_automatic_udls.md) - do not include the user-defined string
literals automatically
- [Modules](../features/modules.md) - C++20 module support
- [Header only](index.md) - including the library
docs/mkdocs/docs/integration/index.md
+1 -1
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@@ -45,7 +45,7 @@ Clang).
You can further use file
[`single_include/nlohmann/json_fwd.hpp`](https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json_fwd.hpp)
for forward declarations, and file
for forward declarations (see [Compile times](compile_times.md)), and file
[`single_include/nlohmann/json_literals.hpp`](https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json_literals.hpp)
for the user-defined string literals if you define
[`JSON_NO_AUTOMATIC_UDLS`](../api/macros/json_no_automatic_udls.md).
docs/mkdocs/docs/integration/migration_guide.md
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@@ -2,11 +2,14 @@
This page collects some guidelines on how to future-proof your code for future versions of this library. For how to
add the library to your project in the first place, see [Integration](index.md), [CMake](cmake.md), or
[Package Managers](package_managers.md).
[Package Managers](package_managers.md). The [roadmap](../community/roadmap.md#version-40) lists what will change in
version 4.0, including the macros that let you try its behavior with a 3.x release; this page describes how to adjust
your code.
## Replace deprecated functions
The following functions have been deprecated and will be removed in the next major version (i.e., 4.0.0). All
The following functions have been deprecated and will be removed in the next major version (i.e., 4.0.0), see the
[roadmap](../community/roadmap.md#removal-of-deprecated-functions) for an overview. All
deprecations are annotated with
[`HEDLEY_DEPRECATED_FOR`](https://nemequ.github.io/hedley/api-reference.html#HEDLEY_DEPRECATED_FOR) to report which
function to use instead.
docs/mkdocs/mkdocs.yml
+3
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@@ -109,6 +109,7 @@ nav:
- integration/cmake.md
- integration/package_managers.md
- integration/pkg-config.md
- integration/compile_times.md
- API Documentation:
- basic_json:
- 'Overview': api/basic_json/index.md
@@ -117,6 +118,7 @@ nav:
- 'accept': api/basic_json/accept.md
- 'array': api/basic_json/array.md
- 'array_t': api/basic_json/array_t.md
- 'as_base_class': api/basic_json/as_base_class.md
- 'at': api/basic_json/at.md
- 'back': api/basic_json/back.md
- 'begin': api/basic_json/begin.md
@@ -365,6 +367,7 @@ nav:
- 'JSON_PRECISE_STREAM_POSITION': api/macros/json_precise_stream_position.md
- 'JSON_SKIP_LIBRARY_VERSION_CHECK': api/macros/json_skip_library_version_check.md
- 'JSON_SKIP_UNSUPPORTED_COMPILER_CHECK': api/macros/json_skip_unsupported_compiler_check.md
- 'JSON_STRICT_BINARY_UTF8': api/macros/json_strict_binary_utf8.md
- 'JSON_STRICT_NUL_HANDLING': api/macros/json_strict_nul_handling.md
- 'JSON_USE_GLOBAL_UDLS': api/macros/json_use_global_udls.md
- 'JSON_USE_IMPLICIT_CONVERSIONS': api/macros/json_use_implicit_conversions.md