mirror of
https://github.com/nlohmann/json.git
synced 2026-10-13 09:47:12 +00:00
132 lines
4.4 KiB
Markdown
132 lines
4.4 KiB
Markdown
# <small>nlohmann::basic_json::</small>operator<=
|
|
|
|
```cpp
|
|
// 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(/* see below */); // (2)
|
|
|
|
template<typename ScalarType>
|
|
bool operator<=(ScalarType lhs, const const_reference rhs) noexcept(/* see below */); // (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 `#!cpp 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 `#!cpp !(rhs < lhs)` (see [**operator<**](operator_lt.md)).
|
|
|
|
2. Compares whether 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
|
|
|
|
1. No-throw guarantee: this function never throws exceptions.
|
|
2. No-throw guarantee if converting the scalar to a JSON value cannot throw, as for numbers, Booleans, and
|
|
`#!cpp nullptr`; the function is `#!cpp noexcept` exactly in that case. Otherwise, it throws what the conversion
|
|
throws, for example `std::bad_alloc` when converting a string, or
|
|
[`out_of_range.410`](../../home/exceptions.md#jsonexceptionout_of_range410) for an enum value not mapped by
|
|
[`NLOHMANN_JSON_SERIALIZE_ENUM_STRICT`](../macros/nlohmann_json_serialize_enum_strict.md).
|
|
|
|
## Complexity
|
|
|
|
Linear.
|
|
|
|
## Notes
|
|
|
|
!!! note "Comparing `NaN`"
|
|
|
|
`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.
|
|
|
|
!!! note "Operator overload resolution"
|
|
|
|
Since C++20 overload resolution will consider the _rewritten candidate_ generated from
|
|
[`operator<=>`](operator_spaceship.md).
|
|
|
|
!!! warning "Deprecation"
|
|
|
|
If [`JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON`](../macros/json_use_legacy_discarded_value_comparison.md) is
|
|
defined to `1`, the library declares a member `#!cpp bool operator<=(const_reference rhs) const noexcept` in
|
|
C++20 mode to emulate the legacy comparison of discarded values. This member is deprecated since version 3.11.0,
|
|
together with the legacy comparison behavior.
|
|
|
|
See the [migration guide](../../integration/migration_guide.md#miscellaneous-functions) for how to update existing
|
|
code.
|
|
|
|
## Examples
|
|
|
|
??? example
|
|
|
|
The example demonstrates comparing several JSON types.
|
|
|
|
```cpp
|
|
#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:
|
|
|
|
```json
|
|
[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<=>**](operator_spaceship.md) 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.
|
|
Made conditionally `#!cpp noexcept` in version 3.13.0; before, a throwing conversion called `std::terminate`.
|