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# nlohmann::basic_json::is_number

    constexpr bool is_number() const noexcept;

This function returns `true` if and only if the JSON value is a number. This includes both integer (signed and unsigned) and floating-point values.

## Return value

`true` if type is number (regardless whether integer, unsigned integer or floating-type), `false` otherwise.

## Exception safety

No-throw guarantee: this member function never throws exceptions.

## Complexity

Constant.

## Possible implementation

    constexpr bool is_number() const noexcept
    {
        return is_number_integer() || is_number_float();
    }

## Examples

Example

The following code exemplifies `is_number()` for all JSON types.

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

    using json = nlohmann::json;

    int main()
    {
        // create JSON values
        json j_null;
        json j_boolean = true;
        json j_number_integer = 17;
        json j_number_unsigned_integer = 12345678987654321u;
        json j_number_float = 23.42;
        json j_object = {{"one", 1}, {"two", 2}};
        json j_array = {1, 2, 4, 8, 16};
        json j_string = "Hello, world";
        json j_binary = json::binary({1, 2, 3});

        // call is_number()
        std::cout << std::boolalpha;
        std::cout << j_null.is_number() << '\n';
        std::cout << j_boolean.is_number() << '\n';
        std::cout << j_number_integer.is_number() << '\n';
        std::cout << j_number_unsigned_integer.is_number() << '\n';
        std::cout << j_number_float.is_number() << '\n';
        std::cout << j_object.is_number() << '\n';
        std::cout << j_array.is_number() << '\n';
        std::cout << j_string.is_number() << '\n';
        std::cout << j_binary.is_number() << '\n';
    }

Output:

    false
    false
    true
    true
    true
    false
    false
    false
    false

## See also

- is_number_integer() check if value is an integer or unsigned integer number
- is_number_unsigned() check if value is an unsigned integer number
- is_number_float() check if value is a floating-point number

## Version history

- Added in version 1.0.0.
- Extended to also return `true` for unsigned integers in 2.0.0.

Last update: May 1, 2022
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