# std::signbit

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< cpp‎ | numeric‎ | math

Defined in header `<cmath>` |  |
| (1) |
bool signbit( float num ); bool signbit( double num ); bool signbit( long double num ); |  | (since C++11) (until C++23)
constexpr bool signbit( /* floating-point-type */ num ); |  | (since C++23)
Additional overloads |  |
Defined in header `<cmath>` |  |
template< class Integer > bool signbit( Integer num ); | (A) | (since C++11) (constexpr since C++23)

1) Determines if the given floating point number num is negative. The library provides overloads for all cv-unqualified floating-point types as the type of the parameter num. (since C++23)
A) Additional overloads are provided for all integer types, which are treated as double.

### Parameters

num | - | floating-point or integer value

### Return value

true if num is negative, false otherwise.

### Notes

This function detects the sign bit of zeroes, infinities, and NaNs. Along with std::copysign, `std::signbit` is one of the only two portable ways to examine the sign of a NaN.

The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their argument num of integer type, std::signbit(num) has the same effect as std::signbit(static_cast<double>(num)).

### Example

Run this code

    #include <cmath>
    #include <iostream>

    int main()
    {
        std::cout << std::boolalpha
                  << "signbit(+0.0) = " << std::signbit(+0.0) << '\n'
                  << "signbit(-0.0) = " << std::signbit(-0.0) << '\n'
                  << "signbit(+nan) = " << std::signbit(+NAN) << '\n'
                  << "signbit(-nan) = " << std::signbit(-NAN) << '\n'
                  << "signbit(+inf) = " << std::signbit(+INFINITY) << '\n'
                  << "signbit(-inf) = " << std::signbit(-INFINITY) << '\n';
    }

Output:

    signbit(+0.0) = false
    signbit(-0.0) = true
    signbit(+nan) = false
    signbit(-nan) = true
    signbit(+inf) = false
    signbit(-inf) = true

### See also

abs(float)fabs fabsf fabsl (C++11)(C++11) | absolute value of a floating point value (\(\small{|x|}\)|x|) (function)
copysign copysignf copysignl (C++11)(C++11)(C++11) | copies the sign of a floating point value (function)

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