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

Defined in header `<cmath>`
Defined in header `<cstdlib>`		(since C++17)
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 argument of type X such that std::is_unsigned<X>::value is true and X cannot be converted to int by integral promotion, the program is ill-formed.

(since C++17)

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';
}

Possible output:

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

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 2735	C++11	`std::abs` was erroneously required to have overloads for integer types returning `double`	removed the requirement

abs(int)labsllabs (C++11)	computes absolute value of an integral value (\|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 `std::abs` to each element of valarray (function template)