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

From cppreference.com
< cpp‎ | numeric‎ | math
 
 
 
Common mathematical functions
Functions
Basic operations
abs(float)fabs
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)(C++11)(C++11)
Exponential functions
(C++11)
(C++11)
(C++11)
(C++11)
Power functions
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Trigonometric and hyperbolic functions
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Error and gamma functions
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Nearest integer floating point operations
(C++11)(C++11)(C++11)
(C++11)
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(C++11)(C++11)(C++11)
Floating point manipulation functions
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Classification/Comparison
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Macro constants
(C++11)(C++11)(C++11)(C++11)(C++11)
 
Defined in header <cmath>
Defined in header <cstdlib>
(1)
float       abs( float num );

double      abs( double num );

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

double      fabs ( double num );

long double fabs ( long double num );
(until C++23)
constexpr /* floating-point-type */
            fabs ( /* floating-point-type */ num );
(since C++23)
float       fabsf( float num );
(3) (since C++11)
(constexpr since C++23)
long double fabsl( long double num );
(4) (since C++11)
(constexpr since C++23)
Additional overloads (since C++11)
Defined in header <cmath>
template< class Integer >
double      fabs ( Integer num );
(A) (since C++11)
(constexpr since C++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 C++23)
A) Additional overloads are provided for all integer types, which are treated as double.
(since C++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.

Contents

[edit] Parameters

num - floating-point or integer value

[edit] Return value

If successful, returns the absolute value of arg (|arg|). The value returned is exact and does not depend on any rounding modes.

[edit] 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.

[edit] 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)).

[edit] Example

#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

[edit] 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

[edit] See also

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