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nlohmann::basic_json::default_object_comparator_t

using default_object_comparator_t = std::less<StringType>;  // until C++14

using default_object_comparator_t = std::less<>;            // since C++14

The default comparator used by object_t.

Since C++14 a transparent comparator is used which prevents unnecessary string construction when looking up a key in an object.

The actual comparator used depends on object_t and can be obtained via object_comparator_t.

Examples

Example

The example below demonstrates the default comparator.

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

using json = nlohmann::json;

int main()
{
    std::cout << std::boolalpha
              << "one < two : " << json::default_object_comparator_t{}("one", "two") << "\n"
              << "three < four : " << json::default_object_comparator_t{}("three", "four") << std::endl;
}

Output:

one < two : true
three < four : false

Version history

  • Added in version 3.11.0.

Last update: October 2, 2022