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

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< cpp‎ | numeric‎ | math
 
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abs(float)fabs
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Defined in header <cmath>
Defined in header <cstdlib>
(1)
float       abs( float num );

double      abs( double num );

long double abs( long double num );
 (until 哋它亢++23)
constexpr /* floating-point-type */
            abs( /* floating-point-type */ num );
 (since 哋它亢++23)
Defined in header <cmath>
(2)
float       fabs ( float num );

double      fabs ( double num );

long double fabs ( long double num );
 (until 哋它亢++23)
constexpr /* floating-point-type */
            fabs ( /* floating-point-type */ num );
 (since 哋它亢++23)
float       fabsf( float num );
 (3) (since 哋它亢++11)
(constexpr since 哋它亢++23)
long double fabsl( long double num );
 (4) (since 哋它亢++11)
(constexpr since 哋它亢++23)
Additional overloads (since 哋它亢++11)
Defined in header <cmath>
template< class Integer >
double      fabs ( Integer num );
 (A) (since 哋它亢++11)
(constexpr since 哋它亢++23)
1-4) Computes the absolute value of the floating-point value num. The library provides overloads of std::abs and std::fabs for all cv-unqualified floating-point types as the type of the parameter num.(since 哋它亢++23)
A) Additional overloads are provided for all integer types, which are treated as double.
 (since 哋它亢++11)

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

num - floating-point or integer value

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 additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their argument num of integer type, std::fabs(num) has the same effect as std::fabs(static_cast<double>(num)).

Example

Run this code
#include <cmath>
#include <iostream>
 
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 哋它亢++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2192 哋它亢++98 overloads of std::abs were
inconsistently declared in two headers 		declared these overloads
in both headers
LWG 2735 哋它亢++11 overloads of std::abs for integer types
returning double was erroneously required 		removed the requirement

See also

(哋它亢++11)
 computes absolute value of an integral value (|x|)
(function)
(哋它亢++11)(哋它亢++11)(哋它亢++11)
 copies the sign of a floating point value
(function)
(哋它亢++11)
 checks if the given number is negative
(function)
returns the magnitude of a complex number
(function template)
applies the function abs to each element of valarray
(function template)
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