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# nlohmann::basic_json::operator<=

    // until C++20
    bool operator<=(const_reference lhs, const_reference rhs) noexcept;   // (1)

    template<typename ScalarType>
    bool operator<=(const_reference lhs, const ScalarType rhs) noexcept;  // (2)

    template<typename ScalarType>
    bool operator<=(ScalarType lhs, const const_reference rhs) noexcept;  // (2)

1. Compares whether one JSON value `lhs` is less than or equal to another JSON value `rhs` according to the following rules:

   - The comparison always yields `false` if (1) either operand is discarded, or (2) either operand is `NaN` and the other operand is either `NaN` or any other number.
   - Otherwise, returns the result of `!(rhs < lhs)` (see operator<).

2. Compares wether a JSON value is less than or equal to a scalar or a scalar is less than or equal to a JSON value 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<ScalarType>::value`

## Parameters

`lhs` (in)
  first value to consider
`rhs` (in)
  second value to consider

## Return value

whether `lhs` is less than or equal to `rhs`

## Exception safety

No-throw guarantee: this function never throws exceptions.

## Complexity

Linear.

## Notes

Comparing `NaN`

`NaN` values are unordered within the domain of numbers. The following comparisons all yield `false`: 1. Comparing a `NaN` with itself. 2. Comparing a `NaN` with another `NaN`. 3. Comparing a `NaN` and any other number.

Operator overload resolution

Since C++20 overload resolution will consider the rewritten candidate generated from `operator<=>`.

## Examples

Example

The example demonstrates comparing several JSON types.

    #include <iostream>
    #include <nlohmann/json.hpp>

    using json = nlohmann::json;

    int main()
    {
        // create several JSON values
        json array_1 = {1, 2, 3};
        json array_2 = {1, 2, 4};
        json object_1 = {{"A", "a"}, {"B", "b"}};
        json object_2 = {{"B", "b"}, {"A", "a"}};
        json number_1 = 17;
        json number_2 = 17.0000000000001L;
        json string_1 = "foo";
        json string_2 = "bar";

        // output values and comparisons
        std::cout << std::boolalpha;
        std::cout << array_1 << " <= " << array_2 << " " << (array_1 <= array_2) << '\n';
        std::cout << object_1 << " <= " << object_2 << " " << (object_1 <= object_2) << '\n';
        std::cout << number_1 << " <= " << number_2 << " " << (number_1 <= number_2) << '\n';
        std::cout << string_1 << " <= " << string_2 << " " << (string_1 <= string_2) << '\n';
    }

Output:

    [1,2,3] <= [1,2,4] true
    {"A":"a","B":"b"} <= {"A":"a","B":"b"} true
    17 <= 17.0000000000001 true
    "foo" <= "bar" false

## See also

- operator<=> comparison: 3-way

## Version history

1. Added in version 1.0.0. Conditionally removed since C++20 in version 3.11.0.
2. Added in version 1.0.0. Conditionally removed since C++20 in version 3.11.0.

Last update: July 31, 2022
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