# nlohmann::basic_json::operator==
```cpp
// until C++20
bool operator==(const_reference lhs, const_reference rhs) noexcept; // (1)
template
bool operator==(const_reference lhs, const ScalarType rhs) noexcept; // (2)
template
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
bool operator==(ScalarType rhs) const noexcept; // (2)
};
```
1. Compares two JSON values for equality according to the following rules:
- Two JSON values are equal if (1) neither value is discarded, or (2) they are of the same type and their stored
values are the same according to their respective `operator==`.
- Integer and floating-point numbers are automatically converted before comparison.
2. Compares a JSON value and a scalar or a scalar and a JSON value for equality by converting the
scalar to a JSON value and comparing both JSON values according to 1.
## Template parameters
`ScalarType`
: a scalar type according to `std::is_scalar::value`
## Parameters
`lhs` (in)
: first value to consider
`rhs` (in)
: second value to consider
## Return value
whether the values `lhs`/`*this` and `rhs` are equal
## Exception safety
No-throw guarantee: this function never throws exceptions.
## Complexity
Linear.
## Notes
!!! note "Comparing special values"
- `NaN` values are unordered within the domain of numbers.
The following comparisons all yield `#!cpp false`:
1. Comparing a `NaN` with itself.
2. Comparing a `NaN` with another `NaN`.
3. Comparing a `NaN` and any other number.
- JSON `#!cpp null` values are all equal.
- Discarded values never compare equal to themselves.
!!! note "Comparing floating-point numbers"
Floating-point numbers inside JSON values numbers are compared with `json::number_float_t::operator==` which is
`double::operator==` by default. To compare floating-point while respecting an epsilon, an alternative
[comparison function](https://github.com/mariokonrad/marnav/blob/master/include/marnav/math/floatingpoint.hpp#L34-#L39)
could be used, for instance
```cpp
template::value, T>::type>
inline bool is_same(T a, T b, T epsilon = std::numeric_limits::epsilon()) noexcept
{
return std::abs(a - b) <= epsilon;
}
```
Or you can self-defined operator equal function like this:
```cpp
bool my_equal(const_reference lhs, const_reference rhs)
{
const auto lhs_type lhs.type();
const auto rhs_type rhs.type();
if (lhs_type == rhs_type)
{
switch(lhs_type)
// self_defined case
case value_t::number_float:
return std::abs(lhs - rhs) <= std::numeric_limits::epsilon();
// other cases remain the same with the original
...
}
...
}
```
!!! note "Comparing different `basic_json` specializations"
Comparing different `basic_json` specializations can have surprising effects. For instance, the result of comparing
the JSON objects
```json
{
"version": 1,
"type": "integer"
}
```
and
```json
{
"type": "integer",
"version": 1
}
```
depends on whether [`nlohmann::json`](../json.md) or [`nlohmann::ordered_json`](../ordered_json.md) is used:
```cpp
--8<-- "examples/operator__equal__specializations.cpp"
```
Output:
```json
--8<-- "examples/operator__equal__specializations.output"
```
## Examples
??? example
The example demonstrates comparing several JSON types.
```cpp
--8<-- "examples/operator__equal.cpp"
```
Output:
```json
--8<-- "examples/operator__equal.output"
```
??? example
The example demonstrates comparing several JSON types against the null pointer (JSON `#!json null`).
```cpp
--8<-- "examples/operator__equal__nullptr_t.cpp"
```
Output:
```json
--8<-- "examples/operator__equal__nullptr_t.output"
```
## Version history
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.