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

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>`
double abs( Integral arg );	(4)	(since C++11)
float fabs( float arg );	(5)
double fabs( double arg );	(6)
long double fabs( long double arg );	(7)
double fabs( Integral arg );	(8)	(since C++11)

1-3,5-7) Computes the absolute value of a floating point value arg.

4,8) A set of overloads or a function template for all combinations of arguments of arithmetic type not covered by (1-3,5-7). If any argument has integral type, it is cast to double. If any other argument is long double, then the return type is long double, otherwise it is double.

For integral arguments, the integral overloads of std::abs may yield a better match than these overloads. 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

Notes

The overloads of std::abs for integer types (4) disagree in return types with the integer overloads of std::abs defined in <cstdlib>, and they also introduce the dangerous overloads of std::abs for unsigned integer types (Defect reports LWG 2192 and LWG 2294).

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

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