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Author SHA1 Message Date
Niels Lohmann 82e7ee29df Use the with_*_t aliases in the remaining tests and docs
#5787 missed the instantiations spelled as `basic_json <` (astyle's
formatting) or ending in the CustomBaseClass argument. Convert them,
including the binary_t.md example pointed out in review.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-09 08:36:38 +02:00
Niels Lohmann d33068da73 Address review comments on the API stability docs and a test comment (#5784)
* Address review comments on #5775 and #5779

Allow new defaulted parameters and new default arguments in the API
stability rules, mention the macro opt-in, and drop the redundant
recompile advice. Describe test-diagnostics-optimized as the regression
test for the fixed #5742.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Document what counts as a breaking change in the API stability rules

Spell out the 3.x compatibility rules in the roadmap: new defaulted
parameters, new default arguments, noexcept/constexpr, template
parameters, parse and dump results, accepted input, key iteration order,
iterator invalidation, implicit conversions, to_json/from_json lookup,
json_sax, value_t enumerators, and documented macros, CMake options and
headers. Also list std::hash values as not part of the public API, and
link the macro overview from the section.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-08 17:44:34 +02:00
Niels Lohmann d8dfc0d0f9 Fix unused-result warnings in the contains and parse_error examples (#5788)
contains(json_pointer) is marked JSON_HEDLEY_WARN_UNUSED_RESULT since #5477,
and parse() has been for longer. The contains example ignored the result in
two try blocks waiting for a parse_error that contains() never throws, so
they printed nothing; print the result for those pointers instead.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-08 16:21:59 +02:00
16 changed files with 62 additions and 243 deletions

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+1 -12
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@@ -64,18 +64,7 @@ values of that type directly to a `basic_json` instance, and they will automatic
rather than arrays:
```cpp
using custom_json = nlohmann::basic_json<
nlohmann::ordered_map, // ObjectType
std::vector, // ArrayType
std::string, // StringType
bool, // BooleanType
std::int64_t, // NumberIntegerType
std::uint64_t, // NumberUnsignedType
double, // NumberFloatType
std::allocator, // AllocatorType
nlohmann::adl_serializer,
std::vector<std::byte> // Custom BinaryType
>;
using custom_json = nlohmann::ordered_json::with_binary_t<std::vector<std::byte>>;
std::vector<std::byte> data{std::byte{1}, std::byte{2}, std::byte{3}};
custom_json j = data; // Creates a binary value, not an array
@@ -137,13 +137,10 @@ Strong exception safety: if an exception occurs, the original value stays intact
When the JSON pointer traverses intermediate levels that don't exist at all yet (not just a missing
leaf), each missing level is created as an array or an object depending on whether the corresponding
pointer token is a valid array index: the token `0`, a sequence of digits that does not begin with `0`,
or the token `-` creates an array, and every other token creates an object. For example, on an
initially `#!json null` value, `/foo/0/0/0` creates nested arrays, while `/foo/one/one/one` creates
nested objects. Tokens such as `01` or the empty token cannot be array indices (cf. RFC 6901, Sect. 4)
and therefore create objects, just as they would if the level already existed as an object. This is not
specified by the JSON Pointer RFC; it is this library's own, intentional disambiguation rule. See also
[JSON Pointer](../../features/json_pointer.md).
pointer token parses as a non-negative integer: a numeric token creates an array, a non-numeric token
creates an object. For example, on an initially `#!json null` value, `/foo/0/0/0` creates nested arrays,
while `/foo/one/one/one` creates nested objects. This is not specified by the JSON Pointer RFC; it is
this library's own, intentional disambiguation rule. See also [JSON Pointer](../../features/json_pointer.md).
!!! warning "Deprecation"
+23 -9
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@@ -36,13 +36,26 @@ work items are tracked in the [GitHub milestones](https://github.com/nlohmann/js
## API stability
Releases follow [semantic versioning](https://semver.org): a minor or patch release of version 3.x does not break code
that uses the public API. In particular, a 3.x release does not:
that uses the public API, unless that code opts in to a change with a macro as described [below](#version-40). In
particular, a 3.x release does not:
- change the signature of a function (its parameter types, return type, number of parameters, or the const-ness of a
member function);
- remove or rename a function or class;
- make breaking changes to the signature of a function: the types or order of its existing parameters, its return type,
its `noexcept` or `constexpr` specifier, or the const-ness of a member function. New parameters may be added if they
have a default value;
- remove or rename a function or class, or change the template parameters of a public class template;
- change which exceptions a function throws, or the [exception ids](../home/exceptions.md);
- change access specifiers or default arguments.
- change access specifiers, or change or remove existing default arguments. New default arguments may be added;
- change the JSON type that a valid input parses to, or the text that `dump()` produces for a valid value;
- accept input that was rejected before, or reject input that was accepted before;
- change the order in which the keys of an object are iterated. The default type sorts keys, and
[`ordered_json`](../api/ordered_json.md) keeps insertion order;
- change when iterators, pointers, or references are invalidated, or the state of a moved-from `basic_json`;
- add or remove implicit conversions from `basic_json`;
- change how `to_json` and `from_json` functions are found, or the behavior of
[`adl_serializer`](../api/adl_serializer/index.md);
- add pure virtual functions to the [`json_sax`](../api/json_sax/index.md) interface;
- remove, rename, renumber, or add enumerators of `value_t`;
- remove or rename a documented macro, CMake option, CMake target, or header, or change what a documented macro does.
Exceptions to these rules, for instance when fixing a bug requires changing the exception a function throws, are
documented in the [release notes](../home/releases.md).
@@ -51,13 +64,14 @@ The following are **not** part of the public API and may change in any release,
- The text of exception messages returned by `what()`. Use the [exception id](../home/exceptions.md) to tell errors
apart.
- The ABI, including `sizeof(basic_json)` and the memory layout of its values. Recompile your code when you upgrade the
library. The [versioned inline namespace](../features/namespace.md) turns mixing versions into a link error.
- The ABI, including `sizeof(basic_json)` and the memory layout of its values. The
[versioned inline namespace](../features/namespace.md) turns mixing versions into a link error.
- The hash values returned by `std::hash` for `basic_json`. Numbers that compare equal still hash equally.
- Everything in namespace `nlohmann::detail`, and macros and type traits that are not documented in the
[API reference](../api/basic_json/index.md).
Changes that would break the public API are only added behind a macro whose default keeps the 3.x behavior, see
[Version 4.0](#version-40).
Breaking changes are only added behind a macro whose default keeps the 3.x behavior. See [Version 4.0](#version-40) and
the [macro overview](../features/macros.md).
## Version 4.0
+1 -13
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@@ -15,19 +15,7 @@ class base_class_with_hidden_members
}
};
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
>;
using json = nlohmann::json::with_base_class_t<base_class_with_hidden_members>;
int main()
{
@@ -19,25 +19,9 @@ int main()
<< j.contains("/array/1"_json_pointer) << '\n'
<< j.contains("/array/-"_json_pointer) << '\n'
<< j.contains("/array/4"_json_pointer) << '\n'
<< j.contains("/baz"_json_pointer) << std::endl;
try
{
// try to use an array index with leading '0'
j.contains("/array/01"_json_pointer);
}
catch (const json::parse_error& e)
{
std::cout << e.what() << '\n';
}
try
{
// try to use an array index that is not a number
j.contains("/array/one"_json_pointer);
}
catch (const json::parse_error& e)
{
std::cout << e.what() << '\n';
}
<< j.contains("/baz"_json_pointer) << '\n'
// an array index with a leading '0' is not found
<< j.contains("/array/01"_json_pointer) << '\n'
// an array index that is not a number is not found
<< j.contains("/array/one"_json_pointer) << std::endl;
}
@@ -5,3 +5,5 @@ true
false
false
false
false
false
+1 -1
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@@ -8,7 +8,7 @@ int main()
try
{
// parsing input with a syntax error
json::parse("[1,2,3,]");
json j = json::parse("[1,2,3,]");
}
catch (const json::parse_error& e)
{
+5 -9
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@@ -473,19 +473,15 @@ class json_pointer
// convert null values to arrays or objects before continuing
if (ptr->is_null())
{
// check if the reference token is a valid array index, that is
// a nonempty sequence of digits without a leading '0'
// (cf. RFC 6901, Sect. 4); tokens that could never be a valid
// array index (such as "01" or "") are treated as object keys
const bool nums = !reference_token.empty()
&& (reference_token.size() == 1 || reference_token[0] != '0')
&& std::all_of(reference_token.begin(), reference_token.end(),
[](const unsigned char x)
// check if the reference token is a number
const bool nums =
std::all_of(reference_token.begin(), reference_token.end(),
[](const unsigned char x)
{
return std::isdigit(x);
});
// change value to an array for array indices or "-" or to object otherwise
// change value to an array for numbers or "-" or to object otherwise
*ptr = (nums || reference_token == "-")
? detail::value_t::array
: detail::value_t::object;
+5 -9
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@@ -20391,19 +20391,15 @@ class json_pointer
// convert null values to arrays or objects before continuing
if (ptr->is_null())
{
// check if the reference token is a valid array index, that is
// a nonempty sequence of digits without a leading '0'
// (cf. RFC 6901, Sect. 4); tokens that could never be a valid
// array index (such as "01" or "") are treated as object keys
const bool nums = !reference_token.empty()
&& (reference_token.size() == 1 || reference_token[0] != '0')
&& std::all_of(reference_token.begin(), reference_token.end(),
[](const unsigned char x)
// check if the reference token is a number
const bool nums =
std::all_of(reference_token.begin(), reference_token.end(),
[](const unsigned char x)
{
return std::isdigit(x);
});
// change value to an array for array indices or "-" or to object otherwise
// change value to an array for numbers or "-" or to object otherwise
*ptr = (nums || reference_token == "-")
? detail::value_t::array
: detail::value_t::object;
+2 -1
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@@ -138,7 +138,8 @@ json_test_set_test_options(test-disabled_exceptions
# only the #972 regression test needs thirdparty/fifo_map on its include path
json_test_set_test_options(test-regression1 LINK_LIBRARIES fifo_map_include)
# GCC's false -Warray-bounds error with JSON_DIAGNOSTICS only shows up when optimizing (#5742).
# Regression test for GCC's false -Warray-bounds error with JSON_DIAGNOSTICS (#5742, fixed in #5585). It only
# showed up when optimizing, so build this test with -O3 and the warning as an error.
# -O3 makes the optimizer-driven warnings of the ci_test_gcc flag set (-Winline,
# -Wsuggest-attribute=...) fire on the library's inline functions; they are not
# what this test checks, so turn them off for it.
+2 -6
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@@ -46,9 +46,7 @@ class huge_binary_t : public std::vector<std::uint8_t>
}
};
using huge_binary_json = nlohmann::basic_json <
std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t,
double, std::allocator, nlohmann::adl_serializer, huge_binary_t, void >;
using huge_binary_json = nlohmann::json::with_binary_t<huge_binary_t>;
// a string type that can be made to report a size beyond INT32_MAX without
// allocating that much memory, so BSON length overflow can be tested for
@@ -96,9 +94,7 @@ class huge_string_t : public std::string
bool pretend_huge = false;
};
using huge_string_json = nlohmann::basic_json <
std::map, std::vector, huge_string_t, bool, std::int64_t, std::uint64_t,
double, std::allocator, nlohmann::adl_serializer, std::vector<std::uint8_t>, void >;
using huge_string_json = nlohmann::json::with_string_t<huge_string_t>;
} // namespace
TEST_CASE("BSON")
+2 -27
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@@ -400,20 +400,7 @@ class base_class_with_hidden_members
std::size_t m_size = 42;
};
using json_with_hidden_base_members =
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
>;
using json_with_hidden_base_members = nlohmann::json::with_base_class_t<base_class_with_hidden_members>;
TEST_CASE("JSON Node as_base_class")
{
@@ -459,19 +446,7 @@ struct const_member_base
const int id = 7; // NOLINT(misc-non-private-member-variables-in-classes)
};
using json_with_const_base = 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>,
const_member_base
>;
using json_with_const_base = nlohmann::json::with_base_class_t<const_member_base>;
// build an array nested @a depth levels deep, with the innermost value 1;
// every level is constructed (never assigned), since const_member_base does
+2 -6
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@@ -26,15 +26,11 @@ namespace
// a BinaryType whose value type is signed: the elements must still be
// processed as the numbers 0..255
using char_binary_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<char>, void >;
using char_binary_json = nlohmann::json::with_binary_t<std::vector<char>>;
#ifdef JSON_HAS_CPP_17
// a BinaryType whose value type is not an integer type at all
using byte_binary_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::byte>, void >;
using byte_binary_json = nlohmann::json::with_binary_t<std::vector<std::byte>>;
#endif
} // namespace
-66
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@@ -466,72 +466,6 @@ TEST_CASE("JSON pointers")
}
}
SECTION("creating intermediate levels")
{
SECTION("tokens that are valid array indices create arrays")
{
json j;
j["/0"_json_pointer] = 1;
CHECK(j == json({1}));
json j2;
j2["/2"_json_pointer] = 1;
CHECK(j2 == json({nullptr, nullptr, 1}));
json j3;
j3["/-"_json_pointer] = 1;
CHECK(j3 == json({1}));
json j4;
j4["/foo/0/0"_json_pointer] = 1;
CHECK(j4 == json({{"foo", {{1}}}}));
}
SECTION("tokens that are no valid array indices create objects")
{
json j;
j["/one"_json_pointer] = 1;
CHECK(j == json({{"one", 1}}));
// leading '0' can never be a valid array index (RFC 6901, Sect. 4)
json j2;
j2["/01"_json_pointer] = 1;
CHECK(j2 == json({{"01", 1}}));
// the empty token is a valid object key, but no valid array index
json j3;
j3["/"_json_pointer] = 1;
CHECK(j3 == json({{"", 1}}));
}
SECTION("creating a level yields the same result as reusing it (#5357)")
{
json j;
j["/a/b/01/d"_json_pointer] = "value";
json j_init = json::object();
j_init["/a/b"_json_pointer] = json::object();
j_init["/a/b/01/d"_json_pointer] = "value";
const json expected = json::parse(R"({"a":{"b":{"01":{"d":"value"}}}})");
CHECK(j == expected);
CHECK(j_init == expected);
// unflatten uses the same key
const json flat = {{"/a/b/01/d", "value"}};
CHECK(flat.unflatten() == expected);
}
SECTION("existing arrays still reject invalid indices")
{
json j = {1, 2, 3};
CHECK_THROWS_WITH_AS(j["/01"_json_pointer],
"[json.exception.parse_error.106] parse error: array index '01' must not begin with '0'", json::parse_error&);
CHECK_THROWS_WITH_AS(j.at("/01"_json_pointer),
"[json.exception.parse_error.106] parse error: array index '01' must not begin with '0'", json::parse_error&);
}
}
SECTION("flatten")
{
json j =
+6 -46
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@@ -2201,10 +2201,7 @@ struct huge_array : std::vector<T, A>
}
};
using huge_array_json = nlohmann::basic_json <
std::map, huge_array, std::string, bool, std::int64_t, std::uint64_t,
double, std::allocator, nlohmann::adl_serializer,
std::vector<std::uint8_t>, void >;
using huge_array_json = nlohmann::json::with_array_t<huge_array>;
TEST_CASE("MessagePack Size above uint32 for array")
{
@@ -2249,18 +2246,7 @@ template<typename K, typename V,
}
};
using huge_object_json = nlohmann::basic_json <
huge_map,
std::vector,
std::string,
bool,
std::int64_t,
std::uint64_t,
double,
std::allocator,
nlohmann::adl_serializer,
std::vector<std::uint8_t>,
void >;
using huge_object_json = nlohmann::json::with_object_t<huge_map>;
TEST_CASE("MessagePack Size above uint32 for object")
{
@@ -2295,18 +2281,7 @@ struct huge_string : std::string
}
};
using huge_string_json = nlohmann::basic_json <
std::map,
std::vector,
huge_string,
bool,
std::int64_t,
std::uint64_t,
double,
std::allocator,
nlohmann::adl_serializer,
std::vector<std::uint8_t>,
void >;
using huge_string_json = nlohmann::json::with_string_t<huge_string>;
TEST_CASE("MessagePack Size above uint32 for string")
{
@@ -2329,18 +2304,7 @@ struct huge_binary : std::vector<std::uint8_t>
}
};
using huge_binary_json = nlohmann::basic_json <
std::map,
std::vector,
std::string,
bool,
std::int64_t,
std::uint64_t,
double,
std::allocator,
nlohmann::adl_serializer,
huge_binary,
void >;
using huge_binary_json = nlohmann::json::with_binary_t<huge_binary>;
TEST_CASE("MessagePack Size above uint32 for binary")
{
@@ -2390,14 +2354,10 @@ class beyond_uint32_string_t : public std::string
}
};
using beyond_uint32_string_json = nlohmann::basic_json <
std::map, std::vector, beyond_uint32_string_t, bool, std::int64_t, std::uint64_t,
double, std::allocator, nlohmann::adl_serializer, std::vector<std::uint8_t>, void >;
using beyond_uint32_string_json = nlohmann::json::with_string_t<beyond_uint32_string_t>;
#endif
using beyond_uint32_binary_json = nlohmann::basic_json <
std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t,
double, std::allocator, nlohmann::adl_serializer, beyond_uint32_binary_t, void >;
using beyond_uint32_binary_json = nlohmann::json::with_binary_t<beyond_uint32_binary_t>;
} // namespace
TEST_CASE("MessagePack lengths beyond UINT32_MAX cannot be serialized")
+1 -10
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@@ -217,16 +217,7 @@ void int_to_string(alt_string& target, std::size_t value)
target = std::to_string(value).c_str();
}
using alt_json = nlohmann::basic_json <
std::map,
std::vector,
alt_string,
bool,
std::int64_t,
std::uint64_t,
double,
std::allocator,
nlohmann::adl_serializer >;
using alt_json = nlohmann::json::with_string_t<alt_string>;
bool operator<(const char* op1, const alt_string& op2) noexcept
{