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

< cpp‎ | numeric‎ | math

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

1-6) Computes the absolute value of a floating point value arg.

7) A set of overloads or a function template accepting an argument of any integral type. Equivalent to (5) (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

#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
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