NAME¶

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

Synopsis¶

Defined in header <cmath>
Defined in header <cstdlib>
float abs( float num );

double abs( double num ); (until C++23)

long double abs( long double num );
constexpr /* floating-point-type */
abs( /* floating-point-type */ (since C++23)
num );
Defined in header <cmath>
float fabs ( float num );

double fabs ( double num ); (until C++23)

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

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 declared these overloads
inconsistently declared in two headers in both headers
overloads of std::abs for integer types
LWG 2735 C++11 returning double was erroneously removed the requirement
required

See also¶

abs(int)
labs computes absolute value of an integral value (\(\small{|x|}\)|x|)
llabs (function)
(C++11)
copysign
copysignf
copysignl copies the sign of a floating point value
(C++11) (function)
(C++11)
(C++11)
signbit checks if the given number is negative
(C++11) (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