# std::abs(float), std::fabs, std::fabsf, std::fabsl

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< cpp‎ | numeric‎ | math

Defined in header `<cmath>` |  |
Defined in header `<cstdlib>` |  |
| (1) |
float abs( float num ); double abs( double num ); long double abs( long double num ); |  | (until C++23)
constexpr /* floating-point-type */ abs( /* floating-point-type */ num ); |  | (since C++23)
Defined in header `<cmath>` |  |
| (2) |
float fabs ( float num ); double fabs ( double num ); long double fabs ( long double num ); |  | (until C++23)
constexpr /* floating-point-type */ fabs ( /* floating-point-type */ num ); |  | (since C++23)
float fabsf( float num ); | (3) | (since C++11) (constexpr since C++23)
long double fabsl( long double num ); | (4) | (since C++11) (constexpr since C++23)
Additional overloads (since C++11) |  |
Defined in header `<cmath>` |  |
template< class Integer > double fabs ( Integer num ); | (A) | (since C++11) (constexpr since C++23)

1-4) Computes the absolute value of the floating-point value num. The library provides overloads of `std::abs` and `std::fabs` 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. | (since C++11)

For integral arguments, the integral overloads of `std::abs` are likely better matches. If `std::abs` is called with an unsigned integral argument that cannot be converted to int by integral promotion, the program is ill-formed.

### Parameters

num | - | floating-point or integer value

### Return value

If successful, returns the absolute value of arg (`|arg|`). The value returned is exact and does not depend on any rounding modes.

### Error handling

This function is not subject to any of the error conditions specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

- If the argument is ±0, +0 is returned
- If the argument is ±∞, +∞ is returned
- If the argument is NaN, NaN is returned

### Notes

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::fabs(num) has the same effect as std::fabs(static_cast<double>(num)).

### Example

Run this code

    #include <cmath>
    #include <iostream>

    int main()
    {
        std::cout << "abs(+3.0) = " << std::abs(+3.0) << '\n'
                  << "abs(-3.0) = " << std::abs(-3.0) << '\n';

        // special values
        std::cout << "abs(-0.0) = " << std::abs(-0.0) << '\n'
                  << "abs(-Inf) = " << std::abs(-INFINITY) << '\n'
                  << "abs(-NaN) = " << std::abs(-NAN) << '\n';
    }

Possible output:

    abs(+3.0) = 3
    abs(-3.0) = 3
    abs(-0.0) = 0
    abs(-Inf) = inf
    abs(-NaN) = nan

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 2192 | C++98 | overloads of `std::abs` were inconsistently declared in two headers | declared these overloads in both headers
LWG 2735 | C++11 | overloads of `std::abs` for integer types returning double was erroneously required | removed the requirement

### See also

abs(int)labs llabs (C++11) | computes absolute value of an integral value (\(\small{|x|}\)|x|) (function)
copysign copysignf copysignl (C++11)(C++11)(C++11) | copies the sign of a floating point value (function)
signbit (C++11) | checks if the given number is negative (function)
abs(std::complex) | returns the magnitude of a complex number (function template)
abs(std::valarray) | applies the function abs to each element of valarray (function template)

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