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nlohmann
2026-10-03 05:43:12 +00:00
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api/basic_json/operator_ne.md
+18 -15
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@@ -9,17 +9,9 @@ bool operator!=(const_reference lhs, const ScalarType rhs) noexcept; // (2)
template<typename ScalarType>
bool operator!=(ScalarType lhs, const const_reference rhs) noexcept; // (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)
};
```
1. Compares two JSON values for inequality. Returns `#!cpp !(lhs == rhs)` (until C++20) or `#!cpp !(*this == rhs)` (since C++20).
1. Compares two JSON values for inequality. Returns `#!cpp !(lhs == rhs)`.
- This means the comparison is simply the logical negation of `operator==`, including for special values like `NaN` and `discarded`.
2. Compares a JSON value and a scalar or a scalar and a JSON value for inequality by converting the scalar to a JSON
@@ -52,6 +44,11 @@ Linear.
## Notes
!!! note "C++20"
Since C++20, `basic_json` declares no `operator!=`. The compiler rewrites `#!cpp a != b` as `#!cpp !(a == b)`
using [`operator==`](operator_eq.md), so the result is the same as described above.
!!! note "Comparing `NaN` and `discarded`"
Since `operator!=` is defined as `!(a == b)`, the behavior for special values follows that of `operator==`:
@@ -61,7 +58,7 @@ Linear.
## Examples
??? example
??? example "Example: (1) compare JSON values"
The example demonstrates comparing several JSON types.
@@ -75,7 +72,7 @@ Linear.
--8<-- "examples/operator__notequal.output"
```
??? example
??? example "Example: (2) compare JSON values with `#!cpp nullptr`"
The example demonstrates comparing several JSON types against the null pointer (JSON `#!json null`).
@@ -89,9 +86,15 @@ Linear.
--8<-- "examples/operator__notequal__nullptr_t.output"
```
## See also
- [operator==](operator_eq.md) comparison: equal
- [operator<=>](operator_spaceship.md) comparison: 3-way (C++20)
## Version history
1. Added in version 1.0.0. Added C++20 member functions in version 3.11.0. Changed in version 3.13.0 to remove
special-casing for `NaN` and `discarded` values; `operator!=` now consistently means `!(a == b)`.
2. Added in version 1.0.0. Added C++20 member functions in version 3.11.0. Changed in version 3.13.0 to remove
special-casing for `NaN` and `discarded` values; `operator!=` now consistently means `!(a == b)`.
1. Added in version 1.0.0. Added a C++20 member function in version 3.11.0. Changed in version 3.13.0 to remove
special-casing for `NaN` and `discarded` values; `operator!=` now consistently means `!(a == b)`. Removed the C++20
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==`.