JSON for Modern C++  3.6.1

◆ operator== [1/3]

template<template< typename U, typename V, typename... Args > class ObjectType = std::map, template< typename U, typename... Args > class ArrayType = std::vector, class StringType = std::string, class BooleanType = bool, class NumberIntegerType = std::int64_t, class NumberUnsignedType = std::uint64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator, template< typename T, typename SFINAE=void > class JSONSerializer = adl_serializer>
bool operator== ( const_reference  lhs,
const_reference  rhs 
)
friend

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 than two NaN values are always treated as unequal.
  • Two JSON null values are equal.
Note
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;
}
NaN values never compare equal to themselves or to other NaN values.
Parameters
[in]lhsfirst JSON value to consider
[in]rhssecond JSON value to consider
Returns
whether the values lhs and rhs are equal
Exception safety
No-throw guarantee: this function never throws exceptions.
Complexity
Linear.
Example
The example demonstrates comparing several JSON types.
1 #include <iostream>
2 #include <nlohmann/json.hpp>
3 
4 using json = nlohmann::json;
5 
6 int main()
7 {
8  // create several JSON values
9  json array_1 = {1, 2, 3};
10  json array_2 = {1, 2, 4};
11  json object_1 = {{"A", "a"}, {"B", "b"}};
12  json object_2 = {{"B", "b"}, {"A", "a"}};
13  json number_1 = 17;
14  json number_2 = 17.000000000000001L;
15  json string_1 = "foo";
16  json string_2 = "bar";
17 
18  // output values and comparisons
19  std::cout << std::boolalpha;
20  std::cout << array_1 << " == " << array_2 << " " << (array_1 == array_2) << '\n';
21  std::cout << object_1 << " == " << object_2 << " " << (object_1 == object_2) << '\n';
22  std::cout << number_1 << " == " << number_2 << " " << (number_1 == number_2) << '\n';
23  std::cout << string_1 << " == " << string_2 << " " << (string_1 == string_2) << '\n';
24 }
basic_json<> json
default JSON class
Definition: json.hpp:871

Output (play with this example online):
[1,2,3] == [1,2,4] false
{"A":"a","B":"b"} == {"A":"a","B":"b"} true
17 == 17.0 true
"foo" == "bar" false
The example code above can be translated with
g++ -std=c++11 -Isingle_include doc/examples/operator__equal.cpp -o operator__equal 
Since
version 1.0.0

Definition at line 18338 of file json.hpp.