basic_json::operator==

bool operator==(const_reference lhs, const_reference rhs) noexcept;

template<typename ScalarType>
bool operator==(const_reference lhs, const ScalarType rhs) noexcept;

template<typename ScalarType>
bool operator==(ScalarType lhs, const const_reference rhs) noexcept;

Compares two JSON values for equality according to the following rules:

• Two JSON values are equal if (1) they are from the same type and (2) their stored values are the same according to their respective operator==.
• Integer and floating-point numbers are automatically converted before comparison. Note that two NaN values are always treated as unequal.
• Two JSON null values are equal.

Template parameters

ScalarType : a scalar type according to std::is_scalar<ScalarType>::value

Parameters

lhs (in) : first value to consider

rhs (in) : second value to consider

Return value

whether the values lhs and rhs are equal

Exception safety

No-throw guarantee: this function never throws exceptions.

Complexity

Linear.

Notes

• Floating-point 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 could be used, for instance

  template<typename T, typename = typename std::enable_if<std::is_floating_point<T>::value, T>::type>
  inline bool is_same(T a, T b, T epsilon = std::numeric_limits<T>::epsilon()) noexcept
  {
      return std::abs(a - b) <= epsilon;
  }
  

  Or you can self-defined operator equal function like this:

  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<float>::epsilon();
              // other cases remain the same with the original
              ...
      }
  ...
  }
  

• NaN values never compare equal to themselves or to other NaN values.

Example

??? example

The example demonstrates comparing several JSON types.
    
```cpp
--8<-- "examples/operator__equal.cpp"
```

Output:

```json
--8<-- "examples/operator__equal.output"
```

Version history

• Added in version 1.0.0.