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 arg ); (1) (constexpr since C++23)
double abs( double arg ); (2) (constexpr since C++23)
long double abs( long double arg ); (3) (constexpr since C++23)
Defined in header <cmath>
float fabs ( float arg ); (4) (constexpr since C++23)
float fabsf( float arg ); (5) (since C++11)
(constexpr since C++23)
double fabs ( double arg ); (6) (constexpr since C++23)
long double fabs ( long double arg ); (7) (constexpr since C++23)
long double fabsl( long double arg ); (8) (since C++11)
(constexpr since C++23)
double fabs ( IntegralType arg ); (9) (since C++11)
(constexpr since C++23)

1-8) Computes the absolute value of a floating point value arg.
9) A set of overloads or a function template accepting an argument of any integral
type. Equivalent to (6) (the argument is cast to 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¶

arg - Value of a floating-point or integral type

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

Example¶

// Run this code

#include <iostream>
#include <cmath>

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
overloads of std::abs were declared these overloads in
LWG 2192 C++98 inconsistently both headers
declared in two headers
overloads of std::abs for integer
LWG 2735 C++11 types removed the requirement
returning double was erroneously
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)