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

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< 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)
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Power functions
(C++11)
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Trigonometric and hyperbolic functions
(C++11)
(C++11)
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Error and gamma functions
(C++11)
(C++11)
(C++11)
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Nearest integer floating point operations
(C++11)(C++11)(C++11)
(C++11)
(C++11)
(C++11)(C++11)(C++11)
Floating point manipulation functions
(C++11)(C++11)
(C++11)
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(C++11)(C++11)
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Classification/Comparison
(C++11)
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Macro constants
(C++11)(C++11)(C++11)(C++11)(C++11)
 
Defined in header <cmath>
Defined in header <cstdlib>
float       abs( float arg );
(1) (constexpr since C++23)
double      abs( double arg );
(2) (constexpr since C++23)
long double abs( long double arg );
(3) (constexpr since C++23)
Defined in header <cmath>
float       fabs ( float arg );
(4) (constexpr since C++23)
float       fabsf( float arg );
(5) (since C++11)
(constexpr since C++23)
double      fabs ( double arg );
(6) (constexpr since C++23)
long double fabs ( long double arg );
(7) (constexpr since C++23)
long double fabsl( long double arg );
(8) (since C++11)
(constexpr since C++23)
double      fabs ( IntegralType arg );
(9) (since C++11)
(constexpr since C++23)
1-8) Computes the absolute value of a floating point value arg.
9) A set of overloads or a function template accepting an argument of any integral type. Equivalent to (6) (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 unsigned integral argument that cannot be converted to int by integral promotion, the program is ill-formed.

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'
              << "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 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

See also

computes absolute value of an integral value (|x|)
(function)
(C++11)(C++11)(C++11)
copies the sign of a floating point value
(function)
(C++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)