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

 

C++

Language

Standard Library Headers

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Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Numerics library

Common mathematical functions

Special mathematical functions

Floating-point environment (C++11)

Complex numbers

Numeric arrays

Pseudo-random number generation

Compile-time rational arithmetic (C++11)

Numeric algorithms

gcd (C++17)

lcm (C++17)

Interpolations

midpoint (C++20)

lerp (C++20)

Generic numeric operations

iota (C++11)

accumulate

inner_product

adjacent_difference

partial_sum

reduce (C++17)

transform_reduce (C++17)

inclusive_scan (C++17)

exclusive_scan (C++17)

transform_inclusive_scan (C++17)

transform_exclusive_scan (C++17)

Bit operations

bit_cast (C++20)

ispow2 (C++20)

ceil2 (C++20)

floor2 (C++20)

log2p1 (C++20)

 

Common mathematical functions

Functions
Basic operations
abs(int)labsllabsimaxabs (C++11) abs(float)fabs divldivlldivimaxdiv (C++11) fmod	remainder (C++11) remquo (C++11) fma (C++11) fmax (C++11) fmin (C++11) fdim (C++11) nannanfnanl (C++11)(C++11)(C++11)
Exponential functions
exp exp2 (C++11) expm1 (C++11)	log log10 log1p (C++11) log2 (C++11)
Power functions
sqrt cbrt (C++11)	hypot (C++11) pow
Trigonometric and hyperbolic functions
sin cos tan asin acos atan atan2	sinh cosh tanh asinh (C++11) acosh (C++11) atanh (C++11)

Error and gamma functions
erf (C++11) erfc (C++11)	lgamma (C++11) tgamma (C++11)
Nearest integer floating point operations
ceil floor roundlroundllround (C++11)(C++11)(C++11)	trunc (C++11) nearbyint (C++11) rintlrintllrint (C++11)(C++11)(C++11)
Floating point manipulation functions
ldexp scalbnscalbln (C++11)(C++11) ilogb (C++11) logb (C++11)	frexp modf nextafternexttoward (C++11)(C++11) copysign (C++11)
Classification/Comparison
fpclassify (C++11) isfinite (C++11) isinf (C++11) isnan (C++11) isnormal (C++11) signbit (C++11)	isgreater (C++11) isgreaterequal (C++11) isless (C++11) islessequal (C++11) islessgreater (C++11) isunordered (C++11)
Macro constants
HUGE_VALFHUGE_VALHUGE_VALL (C++11)(C++11) INFINITY (C++11) NAN (C++11) math_errhandlingMATH_ERRNOMATH_ERREXCEPT (C++11)	FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (C++11)(C++11)(C++11)(C++11)(C++11)

 

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>
	(4)
float       fabs ( float arg );
float       fabsf( float arg );			(since C++11)
double      fabs ( double arg );		(5)
		(6)
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)

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

Run this code

#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

abs(int)labsllabs (C++11)	computes absolute value of an integral value (|x|) (function)
copysigncopysignfcopysignl (C++11)(C++11)(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)