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

Defined in header <cmath>
Defined in header <cstdlib> (since C++17)
float       abs( float arg );
double      abs( double arg );
long double abs( long double arg );
Defined in header <cmath>
float       fabs ( float arg );
float       fabsf( float arg );
(since C++11)
double      fabs ( double arg );
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)


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


#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

See also

computes absolute value of an integral value (|x|)
copies the sign of a floating point value
checks if the given number is negative
returns the magnitude of a complex number
(function template)
applies the function std::abs to each element of valarray
(function template)

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