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Merge develop into fix/ubjson-valueless-budget and avoid MSVC C4127
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
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@@ -67,7 +67,11 @@ basic_json(basic_json&& other) noexcept;
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- **objects**: [`object_t`](object_t.md) and all kinds of compatible associative containers such as `std::map`,
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`std::unordered_map`, `std::multimap`, and `std::unordered_multimap` with a `key_type` compatible to `string_t`
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and a `value_type` from which a `basic_json` value can be constructed.
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- **strings**: `string_t`, string literals, and all compatible string containers can be used.
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- **strings**: `string_t`, string literals, and all compatible string containers can be used. Since version 3.13.0,
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this includes `#!cpp std::u8string` (C++20): its code units are stored as a JSON string and
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[`get<std::u8string>()`](get.md) reads it back (in version 3.12.0, a `#!cpp std::u8string` was stored as an array
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of numbers; `get<std::u8string>()` still accepts such an array). `#!cpp std::u8string_view` and `#!cpp char8_t`
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arrays are not strings; they are stored as arrays of code units.
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!!! note "Rvalue containers are moved from"
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@@ -93,10 +97,18 @@ basic_json(basic_json&& other) noexcept;
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The constructor tries to convert the internal `m_value` of the parameter. Each member value (object, array, string,
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etc.) is serialized via the corresponding `to_json()` overload. For objects and strings, the conversion requires
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that the *target* `basic_json` type's `object_t::key_type` (or `string_t`) be directly constructible from the
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*source* type's corresponding member type via `is_constructible`. If this requirement is not met, the conversion
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does not fail to compile; instead, it silently falls back to the array-conversion path, which represents objects
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as arrays of `[key, value]` pairs and strings as arrays of character codes. This is a known limitation tracked in
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[issue #3425](https://github.com/nlohmann/json/issues/3425).
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*source* type's corresponding member type via `is_constructible`. If this requirement is not met, the result
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depends on the *source* string type:
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- If it is a range of characters (it has `begin()` and `end()`, as `std::string` does), the conversion falls back to
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the array-conversion path, which represents objects as arrays of `[key, value]` pairs and strings as arrays of
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character codes. This result has a different type than the source value, so the constructor's
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[`JSON_ASSERT`](../macros/json_assert.md) fails; with its default definition, `assert`, the program aborts unless
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`NDEBUG` is defined, in which case the array is returned.
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- Otherwise, the conversion does not compile, even though `#!cpp std::is_constructible` reports `#!cpp true`; for
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example, when converting a `basic_json` whose `string_t` is the `alt_string` of the unit tests to `json`.
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This is a known limitation tracked in [issue #3425](https://github.com/nlohmann/json/issues/3425).
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5. Creates a JSON value of type array or object from the passed initializer list `init`. In case `type_deduction` is
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`#!cpp true` (default), the type of the JSON value to be created is deducted from the initializer list `init`
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@@ -130,6 +130,12 @@ overload (3).
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`#!cpp json(true).get<double>()` throw. This is the behavior of all 3.x versions;
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[`basic_json_view::get<T>()`](../basic_json_view/get.md) behaves the same.
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!!! note "`std::u8string` conversions"
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Since version 3.13.0, `#!cpp get<std::u8string>()` (C++20) reads a JSON string; it also accepts an array of numbers,
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the form in which version 3.12.0 stored a `#!cpp std::u8string`. Any other JSON type throws
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[`type_error.302`](../../home/exceptions.md#jsonexceptiontype_error302) ("type must be string or array").
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!!! note "`std::optional` conversions"
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Prior to version 3.13.0, `#!cpp get<std::optional<T>>()` (and other conversions to `std::optional<T>`) failed to
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@@ -102,9 +102,12 @@ objects.
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When converting an object from one `basic_json` specialization to another via the
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[converting constructor](basic_json.md) (overload 4), the target `object_t`'s `key_type` must be
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directly constructible from the source `basic_json`'s `string_t` type (or more generally, from the
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source object's key type). If this requirement is not met, the conversion does not fail; instead,
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the object is silently converted as an array of key-value pairs, which is incorrect. See
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directly constructible from the source object's key type (with the default `std::map`, the source `basic_json`'s
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`string_t`). If this requirement is not met and the source string type is a range of characters, the
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object is converted as an array of key-value pairs, which is incorrect: the converting constructor's
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[`JSON_ASSERT`](../macros/json_assert.md) fails; with its default definition, `assert`, the program aborts unless
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`NDEBUG` is defined, in which case the array is returned. If the source string type is not a range of characters, the
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conversion does not compile at all. See [`basic_json`](basic_json.md) and
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[issue #3425](https://github.com/nlohmann/json/issues/3425) for details and an example.
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## Examples
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@@ -27,6 +27,16 @@ reference operator+=(initializer_list_t init);
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`init` is converted into an object element and added using `operator+=(const typename object_t::value_type&)`.
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Otherwise, `init` is converted to a JSON value and added using `operator+=(basic_json&&)`.
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!!! note "Single braced JSON value"
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For a call such as `#!cpp arr += {obj}`, where the initializer list contains a single JSON value `obj`,
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compilers may disagree unless
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[`JSON_BRACE_INIT_COPY_SEMANTICS`](../macros/json_brace_init_copy_semantics.md) is defined to `1`: GCC, for
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example, selects this overload and appends a single-element array `[obj]`, whereas Clang selects the
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`basic_json` overload and appends a copy of `obj`. With the macro, GCC and Clang both append a copy of `obj`.
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To get a portable result without the macro, write `#!cpp arr += obj` to append a copy, or
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`#!cpp arr += json::array({obj})` to append a single-element array.
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## Iterator invalidation
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For all cases where an element is added to an **array**, a reallocation can happen, in which case all iterators (including
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@@ -60,6 +60,14 @@ Linear.
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2. Comparing a `NaN` with another `NaN`.
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3. Comparing a `NaN` and any other number.
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For arrays and objects, the elements are compared in order. If the comparison reaches a `NaN` and a number (or
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another `NaN`) before any other difference, the result depends on the language standard. Before C++20, the pair
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counts as equivalent and the following elements (or the sizes) decide: for instance, `[NaN] < [1, NaN]` and
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`[1] <= [NaN]` are `#!cpp true`. Since C++20, the whole comparison is unordered, and `<`, `<=`, `>`, and `>=` all
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yield `#!cpp false`. Otherwise (for example `[1, NaN] < [2, NaN]`, or objects whose keys differ), the result is the
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same for all language standards. The same program can therefore order such values differently when it is compiled
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with a different language standard.
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!!! note "Operator overload resolution"
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Since C++20 overload resolution will consider the _rewritten candidate_ generated from
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@@ -60,6 +60,14 @@ Linear.
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2. Comparing a `NaN` with another `NaN`.
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3. Comparing a `NaN` and any other number.
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For arrays and objects, the elements are compared in order. If the comparison reaches a `NaN` and a number (or
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another `NaN`) before any other difference, the result depends on the language standard. Before C++20, the pair
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counts as equivalent and the following elements (or the sizes) decide: for instance, `[NaN] < [1, NaN]` and
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`[1] <= [NaN]` are `#!cpp true`. Since C++20, the whole comparison is unordered, and `<`, `<=`, `>`, and `>=` all
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yield `#!cpp false`. Otherwise (for example `[1, NaN] < [2, NaN]`, or objects whose keys differ), the result is the
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same for all language standards. The same program can therefore order such values differently when it is compiled
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with a different language standard.
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!!! note "Operator overload resolution"
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Since C++20 overload resolution will consider the _rewritten candidate_ generated from
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@@ -61,6 +61,14 @@ Linear.
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2. Comparing a `NaN` with another `NaN`.
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3. Comparing a `NaN` and any other number.
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|
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For arrays and objects, the elements are compared in order. If the comparison reaches a `NaN` and a number (or
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another `NaN`) before any other difference, the result depends on the language standard. Before C++20, the pair
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||||
counts as equivalent and the following elements (or the sizes) decide: for instance, `[NaN] < [1, NaN]` and
|
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`[1] <= [NaN]` are `#!cpp true`. Since C++20, the whole comparison is unordered, and `<`, `<=`, `>`, and `>=` all
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yield `#!cpp false`. Otherwise (for example `[1, NaN] < [2, NaN]`, or objects whose keys differ), the result is the
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same for all language standards. The same program can therefore order such values differently when it is compiled
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||||
with a different language standard.
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|
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!!! note "Operator overload resolution"
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||||
|
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Since C++20 overload resolution will consider the _rewritten candidate_ generated from
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@@ -71,6 +71,14 @@ Linear.
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2. Comparing a `NaN` with another `NaN`.
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3. Comparing a `NaN` and any other number.
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|
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For arrays and objects, the elements are compared in order. If the comparison reaches a `NaN` and a number (or
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another `NaN`) before any other difference, the result depends on the language standard. Before C++20, the pair
|
||||
counts as equivalent and the following elements (or the sizes) decide: for instance, `[NaN] < [1, NaN]` and
|
||||
`[1] <= [NaN]` are `#!cpp true`. Since C++20, the whole comparison is unordered, and `<`, `<=`, `>`, and `>=` all
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yield `#!cpp false`. Otherwise (for example `[1, NaN] < [2, NaN]`, or objects whose keys differ), the result is the
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same for all language standards. The same program can therefore order such values differently when it is compiled
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||||
with a different language standard.
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|
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!!! note "Operator overload resolution"
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||||
|
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Since C++20 overload resolution will consider the _rewritten candidate_ generated from
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@@ -55,6 +55,10 @@ Linear.
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1. Comparing a `NaN` with itself.
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2. Comparing a `NaN` with another `NaN`.
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3. Comparing a `NaN` and any other number.
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- For arrays and objects, the elements are compared in order. If the comparison reaches a `NaN` and a number (or
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another `NaN`) before any other difference, the result is `std::partial_ordering::unordered`. (Without C++20, the
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comparison operators `<`, `<=`, `>`, and `>=` use the comparison of the containers, which treats such a pair as
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equivalent; see [**operator<**](operator_lt.md).)
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## Examples
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@@ -130,11 +130,13 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
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Contiguous inputs (strings, string views, vectors, arrays, pointer ranges) are the fastest to parse. A
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`#!cpp std::istream` comes close: the parser scans the characters its stream buffer holds in bulk, without reading
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ahead, so the stream is left exactly where it would be after reading one character at a time. A `#!cpp FILE*` is
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read one character at a time, but the file is locked only once, so other threads that use the same `FILE` object
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wait until parsing is done. See [input sources and performance](../../features/parsing/index.md#input-sources-and-performance),
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[`JSON_DISABLE_STREAM_BULK_SCAN`](../macros/json_disable_stream_bulk_scan.md), and
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[`JSON_DISABLE_UNLOCKED_FILE_IO`](../macros/json_disable_unlocked_file_io.md).
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ahead, so the stream is left exactly where it would be after reading one character at a time. With glibc
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and the Apple C library, the characters the `#!cpp FILE` holds in its buffer are scanned in bulk like a stream's;
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elsewhere a `#!cpp FILE*` is read one character at a time. Where the C library has unlocked stdio functions, the
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file is locked only once, so other threads that use the same `FILE` object wait until parsing is done, unless
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[`JSON_DISABLE_UNLOCKED_FILE_IO`](../macros/json_disable_unlocked_file_io.md) is defined to `1`. See
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[input sources and performance](../../features/parsing/index.md#input-sources-and-performance) and
|
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[`JSON_DISABLE_STREAM_BULK_SCAN`](../macros/json_disable_stream_bulk_scan.md).
|
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|
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## Examples
|
||||
|
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@@ -311,6 +313,10 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
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it as end of input; planned to become the default in version 4.0.0.
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- Extended empty-input detection to also cover an `std::istream` without a stream buffer, and fixed a crash
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(`std::terminate`) when parsing from an `std::istream` with `eofbit` in its exception mask, in version 3.13.0.
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- Fixed the position that a [`parse_error.101`](../../home/exceptions.md#jsonexceptionparse_error101) reports for an
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unexpected number that is followed by a line feed in version 3.13.0: for the input `1`, line feed, `2`, line feed,
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version 3.12.0 reported "line 2, column 0" and version 3.13.0 reports "line 2, column 1"; for `1 2` and a line feed,
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the report was "line 1, column 0" and is now "line 1, column 3".
|
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- Parsing from an `std::istream` scans the characters in its stream buffer in bulk in version 3.13.0
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||||
([`JSON_DISABLE_STREAM_BULK_SCAN`](../macros/json_disable_stream_bulk_scan.md) restores reading one character at a
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time).
|
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@@ -27,6 +27,16 @@ void push_back(initializer_list_t init);
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`init` is converted into an object element and added using `push_back(const typename object_t::value_type&)`.
|
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Otherwise, `init` is converted to a JSON value and added using `push_back(basic_json&&)`.
|
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|
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!!! note "Single braced JSON value"
|
||||
|
||||
For a call such as `#!cpp arr.push_back({obj})`, where the initializer list contains a single JSON value `obj`,
|
||||
compilers may disagree unless
|
||||
[`JSON_BRACE_INIT_COPY_SEMANTICS`](../macros/json_brace_init_copy_semantics.md) is defined to `1`: GCC, for
|
||||
example, selects this overload and appends a single-element array `[obj]`, whereas Clang selects the
|
||||
`basic_json` overload and appends a copy of `obj`. With the macro, GCC and Clang both append a copy of `obj`.
|
||||
To get a portable result without the macro, write `#!cpp arr.push_back(obj)` to append a copy, or
|
||||
`#!cpp arr.push_back(json::array({obj}))` to append a single-element array.
|
||||
|
||||
## Iterator invalidation
|
||||
|
||||
For all cases where an element is added to an **array**, a reallocation can happen, in which case all iterators (including
|
||||
|
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@@ -124,9 +124,10 @@ consumer `sax` has a super-linear complexity.
|
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|
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A UTF-8 byte order mark is silently ignored.
|
||||
|
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When reading from a `#!c FILE*`, the file is locked while it is parsed. The lock is recursive, so the SAX handler may
|
||||
use the same file with stdio functions, but it must not wait for another thread that uses the same `FILE` object; see
|
||||
[`JSON_DISABLE_UNLOCKED_FILE_IO`](../macros/json_disable_unlocked_file_io.md).
|
||||
When reading from a `#!c FILE*` where the C library has unlocked stdio functions, the file is locked while it is parsed,
|
||||
unless [`JSON_DISABLE_UNLOCKED_FILE_IO`](../macros/json_disable_unlocked_file_io.md) is defined to `1`.
|
||||
The lock is recursive, so the SAX handler may use the same file with stdio functions, but it must not wait for another
|
||||
thread that uses the same `FILE` object.
|
||||
|
||||
## Examples
|
||||
|
||||
|
||||
@@ -67,3 +67,7 @@ Constant.
|
||||
## Version history
|
||||
|
||||
- Added in version 3.12.0.
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||||
- Fixed in version 3.13.0: in version 3.12.0, the start position of a string that contains escape sequences (for
|
||||
example `#!cpp "\n"` or `#!cpp "\u00e4"`) was too large, by the number of bytes the escape sequences add to the
|
||||
source text. The position is now always that of the opening `"`. The "(bytes a-b)" range in the messages of
|
||||
[`JSON_DIAGNOSTICS`](../macros/json_diagnostics.md) was wrong in the same way.
|
||||
@@ -60,9 +60,11 @@ String values are stored as pointers in a `basic_json` type. That is, for any ac
|
||||
When converting a string value from one `basic_json` specialization to another via the
|
||||
[converting constructor](basic_json.md) (overload 4), the target `string_t` must be directly
|
||||
constructible from the source `basic_json`'s `string_t` type. If this requirement is not met, the
|
||||
conversion does not fail; instead, the string is silently converted as an array of character codes,
|
||||
which is incorrect. See [issue #3425](https://github.com/nlohmann/json/issues/3425) for details
|
||||
and an example.
|
||||
conversion depends on the source string type. If it is a range of characters, the string is converted as an array of
|
||||
character codes, which is incorrect: the converting constructor's [`JSON_ASSERT`](../macros/json_assert.md) fails; with
|
||||
its default definition, `assert`, the program aborts unless `NDEBUG` is defined, in which case the array is returned.
|
||||
If the source string type is not a range of characters, the conversion does not compile at all. See
|
||||
[issue #3425](https://github.com/nlohmann/json/issues/3425) for details and an example.
|
||||
|
||||
## Examples
|
||||
|
||||
|
||||
@@ -111,8 +111,9 @@ points apply to every edit:
|
||||
the end, and, with [`number_format::source`](../basic_json_view/number_format.md), keeps the spelling of every
|
||||
number that was not itself edited — see [Editing a document](../../features/json_view/editing.md) for
|
||||
why this matters.
|
||||
- [`read()`](read.md) discards all edits, [`shrink_to_fit()`](shrink_to_fit.md) does not move the node index once
|
||||
there are edits, and [`memory_usage()`](memory_usage.md) includes the memory edits use.
|
||||
- [`read()`](read.md) discards all edits (so its `input` must not be a string obtained from this document),
|
||||
[`shrink_to_fit()`](shrink_to_fit.md) does not move the node index once there are edits, and
|
||||
[`memory_usage()`](memory_usage.md) includes the memory edits use.
|
||||
[`source_offset()`](../basic_json_view/source_offset.md) of a value introduced by an edit is
|
||||
`#!cpp static_cast<std::size_t>(-1)`, the same value it reports for a decoded string.
|
||||
|
||||
|
||||
@@ -113,11 +113,12 @@ How thoroughly `load()` validates `image` before trusting it.
|
||||
`full` (the default)
|
||||
: Checks everything the parser itself guarantees: structure and bounds; that every string is valid UTF-8 (and, for a
|
||||
string still in the source text, that it contains no quote, backslash, or control character); and that every number
|
||||
token is well-formed and matches the value stored for it. Strings and float tokens may share a range only if the
|
||||
ranges are identical (as nodes that share a value do), and never overlap otherwise. Reading and serializing a
|
||||
checked image is safe and always produces valid JSON, exactly as for a parsed document. This is the right choice for
|
||||
an image from anything you do not fully control — a file, a cache shared with other processes, a peer on the
|
||||
network.
|
||||
token is well-formed and matches the value stored for it, and has the type the parser gives it (a float node only
|
||||
for a token with a fraction or an exponent, or an integer that does not fit 64 bits). Strings and float tokens may
|
||||
share a range only if the ranges are identical (as nodes that share a value do), and never overlap otherwise.
|
||||
Reading and serializing a checked image is safe and always produces valid JSON, exactly as for a parsed document.
|
||||
This is the right choice for an image from anything you do not fully control — a file, a cache shared with other
|
||||
processes, a peer on the network.
|
||||
|
||||
`bounds`
|
||||
: Checks structure and bounds only: that every offset and count in the node index stays inside the image. So
|
||||
|
||||
@@ -46,6 +46,34 @@ Linear in the length of the input.
|
||||
Every view taken from `#!cpp *this` before the call — including the previous [`root()`](root.md) — is invalidated,
|
||||
whether or not the new parse succeeds; take fresh views from [`root()`](root.md) afterward.
|
||||
|
||||
!!! warning "`input` must not point into the document itself"
|
||||
|
||||
`read()` releases the document's previous text, its decoded strings, and (for an editable document) its edits
|
||||
*before* it parses `input`. An `input` that is, or points into, any of them violates a precondition: it may seem to
|
||||
work, parse empty or garbled text, be reported by a sanitizer, or read freed memory (undefined behavior).
|
||||
|
||||
This applies to every `string_view` obtained from the document whose characters live in memory that `read()`
|
||||
releases:
|
||||
|
||||
- [`source()`](source.md) of a document that owns its text;
|
||||
- [`get_string()`](../basic_json_view/get_string.md) (also as `get<string_view_t>()` or a `string_view` member of a
|
||||
decoded struct) of a string with escapes, of a string of a document that owns its text, and of an edited string;
|
||||
- [`number_token()`](../basic_json_view/number_token.md) of a number of a document that owns its text, and of a
|
||||
number written by an edit;
|
||||
- the key of an object member (`key()`) if it has escapes, was written by an edit, or the document owns its text.
|
||||
|
||||
It does not apply to a text that the caller owns and the document borrows, nor to the strings, keys, and tokens that
|
||||
are read from such a text unchanged, nor to the decoded strings of a borrowed [image](load.md), which live in the
|
||||
caller's image: `read()` never touches them. To parse JSON that a document holds in a string of its own (for
|
||||
example, JSON embedded in a string value), copy the string first, for example with
|
||||
`#!cpp std::string inner(doc.root()["payload"].get_string()); doc.read(inner);`.
|
||||
|
||||
A debug build (one without `NDEBUG`) checks this with `assert()`: an `input` in the document's text, decoded
|
||||
strings, or image, or in the most recent buffer of strings written by edits, ends the program. (Strings written
|
||||
by earlier edits are not covered.) A release build does not check, to keep the cost of reusing a document at a
|
||||
minimum. The check uses `assert()` directly, not [`JSON_ASSERT`](../macros/json_assert.md), which `json.hpp`
|
||||
undefines at its end.
|
||||
|
||||
`input` is borrowed or owned by the same rules as [`parse()`](parse.md#notes); a document can borrow on one call and
|
||||
own on the next, since ownership is decided freshly each time. An input that is copied (see the table in
|
||||
[`parse()`](parse.md#notes)) is written into the document's previous owned copy, reusing its memory; a moved-in
|
||||
|
||||
@@ -24,6 +24,9 @@ Constant.
|
||||
For a borrowed document, `source()` points directly into the caller's buffer, so it is only valid while that buffer
|
||||
is; see [`owns_source`](owns_source.md).
|
||||
|
||||
The text of a document that owns it must not be passed to [`read()`](read.md) of the same document: `read()` releases
|
||||
an owned text before it parses its input. Copy it first. (A borrowed text belongs to the caller and is not affected.)
|
||||
|
||||
## Examples
|
||||
|
||||
??? example
|
||||
|
||||
@@ -48,8 +48,11 @@ Strong exception safety: if an exception is thrown, there are no changes to the
|
||||
|
||||
May throw `#!cpp std::bad_alloc` if allocating the output string fails. Unlike
|
||||
[`BasicJsonType::dump`](../basic_json/dump.md), there is no `error_handler` parameter and no
|
||||
[`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316): the view only ever holds text the parser
|
||||
already validated as UTF-8, so there is nothing to replace or ignore.
|
||||
[`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316): the parser validated the text the view
|
||||
holds as UTF-8, so there is nothing to replace or ignore. Only a document loaded with
|
||||
[`image_check::bounds` or `image_check::none`](../basic_json_document/load.md#image_check) can still throw it: these do
|
||||
not check the strings, so `dump()` writes such a string as it is, which can be invalid UTF-8 or invalid JSON, and
|
||||
`dump()` with `ensure_ascii` set to `#!cpp true` throws `type_error.316` for invalid UTF-8.
|
||||
|
||||
## Complexity
|
||||
|
||||
|
||||
@@ -46,6 +46,10 @@ The returned [`string_view_t`](index.md#member-types) is valid exactly as long a
|
||||
source text, which for a borrowed document must remain valid **and unmodified** for as long as the document exists,
|
||||
since floating-point values and unescaped strings are read from the source lazily.
|
||||
|
||||
A string with escapes, a string of a document that owns its text, and an edited string must not be passed to
|
||||
[`read()`](../basic_json_document/read.md) of the document it came from: `read()` releases them before it parses its
|
||||
input. Copy the string first. (A string read unchanged from a borrowed text is not affected.)
|
||||
|
||||
## Examples
|
||||
|
||||
??? example
|
||||
|
||||
@@ -38,9 +38,14 @@ by the grammar; trailing zeros in the fraction; the case and sign of the exponen
|
||||
useful precisely where that form must survive — a price or an identifier that must be reproduced exactly, or a
|
||||
number too large for any of `BasicJsonType`'s number types to hold without loss.
|
||||
|
||||
The returned [`string_view_t`](index.md#member-types) always points into the document's
|
||||
[`source()`](../basic_json_document/source.md) text — numbers are never decoded into the document's separate string
|
||||
buffer — and is valid exactly as long as that text is, see the [validity rules](index.md) of `basic_json_view`.
|
||||
The returned [`string_view_t`](index.md#member-types) points into the document's
|
||||
[`source()`](../basic_json_document/source.md) text or, for a number written by an
|
||||
[edit](../basic_json_document/index.md#edits), into storage owned by the document (the token of an edited `NaN` is
|
||||
`nan`). It is valid exactly as long as that text or storage is, see the [validity rules](index.md) of
|
||||
`basic_json_view`. Numbers are never decoded into the document's separate string buffer.
|
||||
|
||||
For the same reason, the token must not be passed to [`read()`](../basic_json_document/read.md) of the document it came
|
||||
from if that document owns its text or the number was written by an edit: `read()` releases both before it parses.
|
||||
|
||||
## Examples
|
||||
|
||||
|
||||
@@ -57,7 +57,9 @@ compared. Two arrays of different [`size()`](size.md) are rejected without visit
|
||||
Only a single number, boolean, or `#!cpp null` value is ever materialized into a `BasicJsonType`, to reuse its
|
||||
`operator==` — for numbers, so that values written differently in the source text but equal in value (e.g. an
|
||||
integer and a floating-point literal) still compare equal, following the same rules `BasicJsonType` does for special
|
||||
values such as `#!cpp NaN`. Constructing one of these scalars never allocates. Strings are compared directly, without
|
||||
values such as `#!cpp NaN`: a `#!cpp NaN` that an [edit](../basic_json_document/set.md) wrote is not equal to itself, so
|
||||
a view of it is not equal to itself either, nor is a view of an array or object that contains one, as for
|
||||
`BasicJsonType`. Constructing one of these scalars never allocates. Strings are compared directly, without
|
||||
allocating, either from the source text on both sides or, for overload 2, against `BasicJsonType`'s own string.
|
||||
Arrays and objects are never materialized at all; only their elements or members are visited, one pair at a time.
|
||||
|
||||
|
||||
@@ -40,6 +40,8 @@ header. See also the [macro overview page](../../features/macros.md).
|
||||
- [**JSON_NO_IO**](json_no_io.md) - switch off functions relying on certain C++ I/O headers
|
||||
- [**JSON_NO_SIMD**](json_no_simd.md) - use only portable code instead of vector instructions (SSE2, SSSE3, NEON)
|
||||
- [**JSON_NO_THREAD_LOCAL**](json_no_thread_local.md) - switch off the use of `thread_local` storage
|
||||
- [**JSON_RECURSION_DEPTH_LIMIT**](json_recursion_depth_limit.md) - set how many nesting levels the operations on a value
|
||||
recurse into on the call stack (default 128)
|
||||
- [**JSON_SKIP_UNSUPPORTED_COMPILER_CHECK**](json_skip_unsupported_compiler_check.md) - do not warn about unsupported compilers
|
||||
- [**JSON_USE_GLOBAL_UDLS**](json_use_global_udls.md) - place user-defined string literals (UDLs) into the global namespace
|
||||
- [**JSON_USE_SIMDUTF**](json_use_simdutf.md) - use the simdutf library to accelerate UTF-8 validation
|
||||
|
||||
@@ -27,9 +27,13 @@ The default value is `0` (disabled — existing behavior is preserved).
|
||||
json j{obj};
|
||||
```
|
||||
|
||||
creates a single-element **array** `[{"key":"value"}]` instead of a copy of `obj`. This behavior is
|
||||
compiler-dependent for older compilers (GCC wrapped, Clang did not), but starting from Clang 20, both compilers
|
||||
behave the same way.
|
||||
creates a single-element **array** `[{"key":"value"}]` instead of a copy of `obj`. For this constructor, the
|
||||
behavior was compiler-dependent for older compilers (GCC wrapped, Clang did not), but starting from Clang 20, both
|
||||
compilers behave the same way.
|
||||
|
||||
The calls `#!cpp arr.push_back({obj})` and `#!cpp arr += {obj}` are still compiler-dependent without the macro,
|
||||
even with Clang 20 and later: GCC converts `{obj}` to a single-element array and appends that array, whereas Clang
|
||||
appends a copy of `obj`. With the macro defined to `1`, both compilers append a copy of `obj`.
|
||||
|
||||
Enabling this macro opts into copy/move semantics for this case
|
||||
(see [#5074](https://github.com/nlohmann/json/issues/5074)).
|
||||
|
||||
@@ -125,3 +125,5 @@ When the macro is not defined, the library will define it to its default value.
|
||||
## Version history
|
||||
|
||||
- Added in version 3.12.0.
|
||||
- Fixed in version 3.13.0: in version 3.12.0, [`start_pos()`](../basic_json/start_pos.md) of a string that contains
|
||||
escape sequences was too large; it is now the position of the opening `"`.
|
||||
@@ -45,6 +45,7 @@ Copying and comparing fall back to working without the call stack there, as they
|
||||
|
||||
## See also
|
||||
|
||||
- [`JSON_RECURSION_DEPTH_LIMIT`](json_recursion_depth_limit.md) - set how many nesting levels the operations recurse into
|
||||
- [FAQ: Thread safety](../../home/faq.md#thread-safety) - thread-safety guarantees of the library
|
||||
- [Supported Macros](../../features/macros.md) - guide to all supported macros
|
||||
|
||||
|
||||
@@ -0,0 +1,307 @@
|
||||
# JSON_RECURSION_DEPTH_LIMIT
|
||||
|
||||
```cpp
|
||||
#define JSON_RECURSION_DEPTH_LIMIT /* value */
|
||||
```
|
||||
|
||||
This macro sets how many nesting levels the operations that walk a value recurse into on the call stack. Beyond that,
|
||||
they continue with an explicit stack on the heap. The value is an integer constant from `0` to `254`; the default is
|
||||
`128`.
|
||||
|
||||
The operations are copying a value, comparing two values, serializing with [`dump`](../basic_json/dump.md) or
|
||||
[`operator<<`](../operator_ltlt.md), hashing with `std::hash`, [`merge_patch`](../basic_json/merge_patch.md),
|
||||
[`update`](../basic_json/update.md) with `merge_objects`, [`diff`](../basic_json/diff.md),
|
||||
[`merge_diff`](../basic_json/merge_diff.md), converting a value to another specialization of `basic_json`, destroying a
|
||||
value, and the binary writers [`to_cbor`](../basic_json/to_cbor.md),
|
||||
[`to_msgpack`](../basic_json/to_msgpack.md), [`to_ubjson`](../basic_json/to_ubjson.md),
|
||||
[`to_bjdata`](../basic_json/to_bjdata.md), and [`to_bon8`](../basic_json/to_bon8.md). They share this one limit; none
|
||||
has
|
||||
a limit of its own. Recursing is the fastest way to walk a value, but a value nested deeply enough would exhaust the
|
||||
call
|
||||
stack, so the library recurses only as far as the limit and finishes the levels below with an explicit stack. This is
|
||||
what makes all of them safe for untrusted input
|
||||
(see [Nesting depth](../../features/parsing/untrusted_input.md#nesting-depth)). Parsing, the binary readers,
|
||||
[`flatten`](../basic_json/flatten.md), [`unflatten`](../basic_json/unflatten.md), and
|
||||
[`to_bson`](../basic_json/to_bson.md) always use an explicit stack and do not depend on the macro. The lockstep
|
||||
comparison of two [`json_view`](../basic_json_view/index.md) documents has a fixed bound of its own, 48 levels,
|
||||
and does not depend on it either.
|
||||
|
||||
The call stack that these operations need grows with the limit: roughly *a few kilobytes plus a cost per level times the
|
||||
limit*, where the cost per level is up to about 2.3 KiB in an unoptimized and up to about 0.5 KiB in an optimized build
|
||||
(see [Stack needed](#stack-needed)). The default of `128` levels is tuned for threads with ordinary stacks of a few
|
||||
hundred kilobytes or more. Set a lower limit if your threads have small stacks (RTOS tasks, fibers, threads of the musl
|
||||
C
|
||||
library, which has a default stack of 128 KiB), or a higher limit to trade stack for speed on deeply nested values.
|
||||
|
||||
The macro changes only how much stack is used and how fast the operations are. It never changes a result: every
|
||||
operation returns the same value for every setting of the limit, for values nested less deeply than the limit as well as
|
||||
for values nested more deeply.
|
||||
|
||||
## Default definition
|
||||
|
||||
The default value is `128`.
|
||||
|
||||
```cpp
|
||||
#define JSON_RECURSION_DEPTH_LIMIT 128
|
||||
```
|
||||
|
||||
When the macro is not defined, the library defines it to its default value.
|
||||
|
||||
## Notes
|
||||
|
||||
!!! note "Allowed values"
|
||||
|
||||
The value must be an integer constant expression from `0` to `254`; any other value (a negative number, a number
|
||||
above `254`, a floating-point number such as `254.0`, or `true` or `false`) is rejected at compile time with an
|
||||
error message that names the macro. A character of any character type (`'a'`, `L'a'`, `u8'a'`, ...) is rejected,
|
||||
too, although it is an integer.
|
||||
|
||||
- `0` is allowed, and means that every operation uses its explicit stack from the first level on and no operation
|
||||
recurses over the nesting of a value at all. That needs a constant amount of call stack (at most 16 KiB in the
|
||||
measurements below, for a value nested 20,000 levels deep) and is the setting for tiny stacks, at the price of
|
||||
speed (see [Speed](#speed)).
|
||||
- `254` is the largest allowed value. Copying a value and comparing two values (with `<=>`, or with the operators on
|
||||
objects and arrays of a custom type) cannot pass the depth down as an argument, because the signatures of the
|
||||
copy constructor and the operators are fixed. They count the levels they have descended into in a variable of type
|
||||
`#!cpp std::uint8_t` that exists once per thread (see [`JSON_NO_THREAD_LOCAL`](json_no_thread_local.md)). Only
|
||||
the levels that are descended into are counted, so the count never exceeds the limit, not even when user code (a
|
||||
copy constructor of a custom base class, say) copies a value while a copy is going on. A byte holds `255` at
|
||||
most, and the limit stays below that, so that the count cannot wrap around. (More levels would hardly be
|
||||
useful: `254` levels need up to 576 KiB of stack in an unoptimized build already, twice as much as the
|
||||
default.)
|
||||
|
||||
### Stack needed
|
||||
|
||||
The tables show the smallest stack that an operation needs, in KiB, at several limits, on a value that is nested
|
||||
more deeply than the limit (limit + 10 levels). Each cell shows the result for Clang (Apple clang 21) and for
|
||||
GCC 16, separated by a slash; both measured on macOS with arm64, compiling in C++20 mode. The operations run in a
|
||||
thread whose stack has the size given, and are not given any stack that they do not need: the value is built, and
|
||||
the result destroyed, outside of that thread. Stacks can only be set in steps of 16 KiB (the page size), so `16`
|
||||
means "16 KiB or less". A row stands for all operations listed; the table shows the largest value among them.
|
||||
|
||||
Unoptimized (`-O0`):
|
||||
|
||||
| Operation | limit 16 | limit 32 | limit 64 | limit 128 | limit 254 |
|
||||
|---|---:|---:|---:|---:|---:|
|
||||
| `dump()` and `dump(indent)`, `operator<<` | 48 / 32 | 80 / 64 | 144 / 128 | 288 / 256 | 576 / 512 |
|
||||
| copy construction and assignment | 32 / 16 | 48 / 32 | 112 / 80 | 224 / 144 | 432 / 304 |
|
||||
| `==` | 16 / 16 | 16 / 16 | 16 / 16 | 48 / 32 | 96 / 48 |
|
||||
| `<=>` (C++20) | 16 / 16 | 16 / 16 | 32 / 32 | 64 / 64 | 144 / 128 |
|
||||
| `std::hash` | 16 / 16 | 16 / 16 | 32 / 32 | 80 / 64 | 160 / 128 |
|
||||
| `merge_patch`, `update(j, true)`, `patch` | 32 / 16 | 48 / 32 | 112 / 80 | 224 / 144 | 432 / 304 |
|
||||
| `diff` | 16 / 16 | 16 / 16 | 32 / 32 | 64 / 48 | 144 / 96 |
|
||||
| `merge_diff` | 16 / 16 | 48 / 32 | 80 / 48 | 176 / 112 | 352 / 224 |
|
||||
| `to_cbor`, `to_msgpack` | 16 / 16 | 32 / 16 | 64 / 32 | 112 / 80 | 224 / 160 |
|
||||
| `to_ubjson`, `to_bjdata` | 16 / 16 | 16 / 16 | 48 / 32 | 96 / 64 | 176 / 112 |
|
||||
| `to_bon8` | 16 / 16 | 16 / 16 | 16 / 16 | 32 / 16 | 64 / 48 |
|
||||
| conversion to another `basic_json` type | 32 / 16 | 64 / 32 | 112 / 80 | 224 / 144 | 448 / 304 |
|
||||
| destruction | 16 / 16 | 16 / 16 | 16 / 16 | 16 / 16 | 32 / 32 |
|
||||
|
||||
Optimized (`-O2`):
|
||||
|
||||
| Operation | limit 16 | limit 32 | limit 64 | limit 128 | limit 254 |
|
||||
|---|---:|---:|---:|---:|---:|
|
||||
| `dump()` and `dump(indent)`, `operator<<` | 16 / 16 | 16 / 16 | 16 / 16 | 16 / 16 | 32 / 32 |
|
||||
| copy construction and assignment | 16 / 16 | 16 / 16 | 16 / 16 | 32 / 32 | 64 / 48 |
|
||||
| `==` | 16 / 16 | 16 / 16 | 16 / 16 | 16 / 16 | 16 / 16 |
|
||||
| `<=>` (C++20) | 16 / 16 | 16 / 16 | 16 / 16 | 16 / 16 | 48 / 16 |
|
||||
| `std::hash` | 16 / 16 | 16 / 16 | 16 / 16 | 32 / 48 | 80 / 80 |
|
||||
| `merge_patch`, `update(j, true)`, `patch` | 16 / 16 | 16 / 16 | 16 / 16 | 32 / 32 | 64 / 48 |
|
||||
| `diff` | 16 / 16 | 16 / 16 | 16 / 32 | 48 / 48 | 96 / 112 |
|
||||
| `merge_diff` | 16 / 16 | 16 / 16 | 16 / 16 | 48 / 32 | 96 / 64 |
|
||||
| `to_cbor`, `to_msgpack` | 16 / 16 | 16 / 16 | 16 / 16 | 16 / 16 | 16 / 16 |
|
||||
| `to_ubjson`, `to_bjdata` | 16 / 16 | 16 / 16 | 16 / 16 | 32 / 32 | 64 / 64 |
|
||||
| `to_bon8` | 16 / 16 | 16 / 16 | 16 / 16 | 16 / 32 | 32 / 64 |
|
||||
| conversion to another `basic_json` type | 16 / 16 | 16 / 16 | 16 / 16 | 32 / 48 | 64 / 96 |
|
||||
| destruction | 16 / 16 | 16 / 16 | 16 / 16 | 16 / 16 | 16 / 16 |
|
||||
|
||||
With a limit of `0`, every operation in the tables ran in a 16 KiB stack at `-O0` (Clang and GCC), on a value nested
|
||||
20,000 levels deep. The operations that do not depend on the macro (`flatten`, `unflatten`, `to_bson`) needed
|
||||
16 KiB or less at every limit.
|
||||
|
||||
The rule of thumb is
|
||||
|
||||
> stack needed ≈ a few KiB + cost per level × limit
|
||||
|
||||
with a cost per level of up to 2.3 KiB (`dump` at `-O0` with Clang; 2.1 KiB with GCC), 1.7 KiB for copying and merging
|
||||
(1.3 KiB with GCC), and 0.1 to 0.5 KiB for most other operations at `-O0`; and 0.5 KiB or less at `-O2`. The numbers
|
||||
come from the difference between the limits `128` and `254` in the tables, so they are rough: other compilers,
|
||||
other targets (the frames of x86-64 code are about as large), other standard libraries, `JSON_DIAGNOSTICS`, and
|
||||
sanitizers change them. Measure with your own tool chain (see the example below) rather than relying on the tables.
|
||||
The stack that your own code and the operating system need comes on top of these numbers.
|
||||
|
||||
Which limit to choose, for the stack that you can spare for the library (the largest limit of those measured
|
||||
for which the slowest operation needs at most that much):
|
||||
|
||||
| Stack for the library | optimized (`-O2`) | unoptimized (`-O0`) |
|
||||
|---|---:|---:|
|
||||
| 32 KiB | 64 | 0 |
|
||||
| 64 KiB | 128 | 16 |
|
||||
| 128 KiB (the default stack of threads on musl) | 254 | 32 |
|
||||
| 256 KiB | 254 | 64 |
|
||||
| 512 KiB | 254 | 128 |
|
||||
| 1 MiB or more | 254 | 254 |
|
||||
|
||||
### Speed
|
||||
|
||||
Operations are faster the more of a value they handle with plain recursion. The levels below the limit are handled with
|
||||
an explicit stack, which has to be kept on the heap and costs more per level. The macro therefore trades speed against
|
||||
stack.
|
||||
|
||||
The table shows the time of copying a value (including destroying the copy), of `==` on two equal values, of `dump`, and
|
||||
of `std::hash` for several limits, relative to the default of `128` (`1.00` means the same time; more is slower). It was
|
||||
measured with Clang 21 at `-O2` in C++17 mode on macOS with arm64, as the best of seven runs of each setting (two
|
||||
rounds, best of both). The documents are ordinary JSON files that are nested 7 (`canada.json`), 8
|
||||
(`citm_catalog.json`), 10 (`twitter.json`), and 2 levels deep (`jeopardy.json`); the other values are one array or object
|
||||
with one member per level, nested 1,000 and 100,000 levels deep. The absolute time at the limit `128` is given in the
|
||||
third column. Differences of up to about 0.1 are noise: a different limit changes the layout of the compiled code, and
|
||||
timings of the same binary vary by about as much. The slow columns (limits 0 and 1) vary more: repeating `std::hash` on
|
||||
`canada.json` gave 1.27 to 1.30 for limit 0 and 1.4 to 1.9 for limit 1, so read the cells of those two columns as
|
||||
accurate to about 0.3.
|
||||
|
||||
| Value | Operation | limit 128 (absolute) | limit 0 | limit 1 | limit 16 | limit 254 |
|
||||
|---|---|---:|---:|---:|---:|---:|
|
||||
| `canada.json` (2.1 MB) | copy | 3.5 ms | 1.80 | 1.80 | 0.99 | 1.00 |
|
||||
| `canada.json` (2.1 MB) | `==` | 350.5 µs | 2.36 | 2.38 | 1.00 | 0.99 |
|
||||
| `canada.json` (2.1 MB) | `dump` | 2.4 ms | 1.11 | 1.11 | 1.00 | 1.00 |
|
||||
| `canada.json` (2.1 MB) | `std::hash` | 920.2 µs | 1.33 | 1.59 | 1.00 | 1.00 |
|
||||
| `citm_catalog.json` (1.7 MB) | copy | 1.8 ms | 1.38 | 1.36 | 1.00 | 0.99 |
|
||||
| `citm_catalog.json` (1.7 MB) | `==` | 275.5 µs | 1.31 | 1.31 | 0.99 | 1.00 |
|
||||
| `citm_catalog.json` (1.7 MB) | `dump` | 314.6 µs | 1.24 | 1.23 | 1.00 | 1.00 |
|
||||
| `citm_catalog.json` (1.7 MB) | `std::hash` | 309.1 µs | 1.77 | 1.42 | 1.06 | 1.05 |
|
||||
| `twitter.json` (0.6 MB) | copy | 865.7 µs | 1.45 | 1.47 | 1.01 | 1.00 |
|
||||
| `twitter.json` (0.6 MB) | `==` | 135.8 µs | 1.26 | 1.23 | 1.00 | 1.00 |
|
||||
| `twitter.json` (0.6 MB) | `dump` | 224.6 µs | 1.12 | 1.12 | 1.01 | 1.00 |
|
||||
| `twitter.json` (0.6 MB) | `std::hash` | 132.9 µs | 1.28 | 1.27 | 1.03 | 1.04 |
|
||||
| `jeopardy.json` (53 MB) | copy | 111.1 ms | 1.22 | 1.25 | 1.00 | 1.00 |
|
||||
| `jeopardy.json` (53 MB) | `==` | 23.5 ms | 1.29 | 1.53 | 1.07 | 1.00 |
|
||||
| `jeopardy.json` (53 MB) | `dump` | 33.2 ms | 1.14 | 1.34 | 1.03 | 1.01 |
|
||||
| `jeopardy.json` (53 MB) | `std::hash` | 19.9 ms | 1.17 | 1.52 | 1.05 | 1.00 |
|
||||
| arrays, 1,000 levels | copy | 69.9 µs | 0.95 | 0.98 | 0.92 | 0.99 |
|
||||
| arrays, 1,000 levels | `==` | 10.4 µs | 1.02 | 1.01 | 0.96 | 1.00 |
|
||||
| arrays, 1,000 levels | `dump` | 9.6 µs | 0.97 | 0.96 | 0.97 | 1.06 |
|
||||
| arrays, 1,000 levels | `std::hash` | 16.9 µs | 1.00 | 1.01 | 1.01 | 0.98 |
|
||||
| objects, 1,000 levels | copy | 77.1 µs | 0.98 | 0.97 | 0.97 | 1.03 |
|
||||
| objects, 1,000 levels | `==` | 12.0 µs | 0.96 | 0.95 | 0.95 | 1.07 |
|
||||
| objects, 1,000 levels | `dump` | 12.6 µs | 0.97 | 0.95 | 0.98 | 1.01 |
|
||||
| objects, 1,000 levels | `std::hash` | 17.3 µs | 0.99 | 1.01 | 0.98 | 1.00 |
|
||||
| arrays, 100,000 levels | copy | 6.4 ms | 1.00 | 1.00 | 1.00 | 1.00 |
|
||||
| arrays, 100,000 levels | `==` | 1.1 ms | 1.01 | 1.03 | 1.00 | 1.06 |
|
||||
| arrays, 100,000 levels | `dump` | 917.9 µs | 1.01 | 1.01 | 1.02 | 1.01 |
|
||||
| arrays, 100,000 levels | `std::hash` | 1.7 ms | 1.04 | 1.05 | 0.99 | 0.99 |
|
||||
| objects, 100,000 levels | copy | 7.5 ms | 0.99 | 1.02 | 1.01 | 0.99 |
|
||||
| objects, 100,000 levels | `==` | 1.3 ms | 1.02 | 1.09 | 1.08 | 0.96 |
|
||||
| objects, 100,000 levels | `dump` | 1.2 ms | 1.06 | 0.99 | 1.01 | 0.99 |
|
||||
| objects, 100,000 levels | `std::hash` | 1.8 ms | 1.00 | 1.00 | 1.00 | 1.00 |
|
||||
|
||||
The results are as follows.
|
||||
|
||||
- A limit of `16` or more does not change the speed of ordinary documents (differences are within noise), because they
|
||||
are not nested more deeply than that anyway. A document nested more deeply than the limit is walked partly with the
|
||||
explicit stack.
|
||||
- A limit of `0` or `1` makes the operations on ordinary documents 1.1 to 2.4 times as slow, because even their first
|
||||
levels are handled with the explicit stack. The slowdown is largest for `==` on a document of many small containers
|
||||
(`canada.json`: 2.4 times) and for copying (up to 1.8 times).
|
||||
- For values that are nested far more deeply than any limit (1,000 and 100,000 levels deep), the limit makes no
|
||||
measurable difference: almost all of the levels are handled with the explicit stack for every setting.
|
||||
Raising the limit gains nothing for them, and lowering it costs nothing.
|
||||
|
||||
!!! note "Other macros"
|
||||
|
||||
- With [`JSON_NO_THREAD_LOCAL`](json_no_thread_local.md) defined (or for Clang targeting MinGW, where the library
|
||||
defines it by itself), copying and comparing never descend, so for them the limit does not matter. The other
|
||||
operations still recurse as many levels as the limit says. The range of the limit is the same.
|
||||
- The macro is not part of the [ABI tag](../../features/namespace.md), as `JSON_NO_THREAD_LOCAL` is not, and it is
|
||||
not undefined at the end of `json.hpp`.
|
||||
|
||||
!!! warning "Use the same value in every translation unit"
|
||||
|
||||
All translation units of a program that include the library must define the same value. Otherwise, the program
|
||||
violates the One Definition Rule: the function `nlohmann::detail::recursion_depth_limit()` and all the functions
|
||||
that use it are defined differently in different translation units. Which limit a call uses then depends on which
|
||||
functions the compiler inlined (an inlined copy uses the value of its own translation unit) and which out-of-line
|
||||
copy of each remaining function the linker kept, which is not specified. A function compiled with one value can
|
||||
call a function compiled with another, so a single operation can mix both limits.
|
||||
|
||||
Mixing values cannot corrupt the byte per thread that counts the levels of copying and comparing: each limit
|
||||
is at most `254`, and all of them stop counting at their own limit, so the count never exceeds `254`, whichever
|
||||
translation unit's definition runs. The counter exists once per thread and `basic_json` specialization, and is
|
||||
shared by all translation units. Nor can mixing values change any result, as no result depends on the limit. What
|
||||
changes is how much stack is used and how fast the operations are. Nevertheless, avoid it: the program has undefined
|
||||
behavior as far as the C++ standard is concerned.
|
||||
|
||||
## Examples
|
||||
|
||||
??? example "Example: lower the limit"
|
||||
|
||||
The example nests an array 5,000 levels deep. With the limit set to 16, the library recurses over the first 16
|
||||
levels
|
||||
and over the rest uses an explicit stack. The results are those of the default limit.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/json_recursion_depth_limit.cpp"
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```
|
||||
--8<-- "examples/json_recursion_depth_limit.output"
|
||||
```
|
||||
|
||||
??? example "Example: find out how much stack an operation needs"
|
||||
|
||||
The program runs `dump()` on a value nested `depth` levels deep in a thread with a stack of `kib` KiB. Compile it
|
||||
with the options and the limit that you use, e.g. `-DJSON_RECURSION_DEPTH_LIMIT=64`, run it with `depth` set to the
|
||||
limit plus 10 and decreasing values of `kib` (the stack size must be a multiple of the page size, often 4 or 16
|
||||
KiB),
|
||||
and note the smallest stack with which it still finishes. That is how the tables above were measured.
|
||||
|
||||
```cpp
|
||||
#include <cstdlib>
|
||||
#include <iostream>
|
||||
#include <string>
|
||||
#include <utility>
|
||||
#include <pthread.h>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
static nlohmann::json value;
|
||||
|
||||
static void* run(void*)
|
||||
{
|
||||
std::cout << "dump() ok, " << value.dump().size() << " bytes\n";
|
||||
return nullptr;
|
||||
}
|
||||
|
||||
int main(int argc, char** argv)
|
||||
{
|
||||
const int depth = std::atoi(argv[1]);
|
||||
const std::size_t kib = static_cast<std::size_t>(std::atoi(argv[2]));
|
||||
|
||||
// built on the main thread, without recursion
|
||||
value = 1;
|
||||
for (int i = 0; i < depth; ++i)
|
||||
{
|
||||
nlohmann::json outer = nlohmann::json::array();
|
||||
outer.push_back(std::move(value));
|
||||
value = std::move(outer);
|
||||
}
|
||||
|
||||
pthread_attr_t attr;
|
||||
pthread_attr_init(&attr);
|
||||
pthread_attr_setstacksize(&attr, kib * 1024);
|
||||
pthread_t thread;
|
||||
pthread_create(&thread, &attr, run, nullptr);
|
||||
pthread_join(thread, nullptr);
|
||||
}
|
||||
```
|
||||
|
||||
## See also
|
||||
|
||||
- [Nesting depth](../../features/parsing/untrusted_input.md#nesting-depth) - how the library handles deeply nested
|
||||
values
|
||||
- [`JSON_NO_THREAD_LOCAL`](json_no_thread_local.md) - switch off the use of `thread_local` storage
|
||||
- [Supported Macros](../../features/macros.md) - guide to all supported macros
|
||||
|
||||
## Version history
|
||||
|
||||
- Added in version 3.13.0.
|
||||
@@ -93,7 +93,7 @@ The default value is `0` (disabled, the behavior of version 3.12.0 and earlier i
|
||||
## See also
|
||||
|
||||
- [Binary formats](../../features/binary_formats/index.md) - overview of the supported binary formats
|
||||
- [`from_cbor`](../basic_json/from_cbor.md) - also affected when parsing CBOR strings
|
||||
- [`from_cbor`](../basic_json/from_cbor.md) - not affected by the macro; pass `error_handler` to validate CBOR strings
|
||||
- [`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
|
||||
|
||||
Reference in new issue
Block a user