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

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)

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

#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

abs(int)labsllabs (C++11)	computes absolute value of an integral value (\(\small{\|x\|}\)\|x\|) (function)
copysigncopysignfcopysignl (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)
C documentation for `fabs`