std::abs, std::labs, std::llabs, std::imaxabs

Defined in header `<cstdlib>`
Defined in header `<cmath>`
int abs( int num );	(1)	(constexpr since C++23)
long abs( long num );	(2)	(constexpr since C++23)
long long abs( long long num );	(3)	(since C++11) (constexpr since C++23)
Defined in header `<cstdlib>`
long labs( long num );	(4)	(constexpr since C++23)
long long llabs( long long num );	(5)	(since C++11) (constexpr since C++23)
Defined in header `<cinttypes>`
std::intmax_t abs( std::intmax_t num );	(6)	(since C++11) (constexpr since C++23)
std::intmax_t imaxabs( std::intmax_t num );	(7)	(since C++11) (constexpr since C++23)

Computes the absolute value of the integer number num. The behavior is undefined if the result cannot be represented by the return type.

If std::abs is called with an unsigned integral argument that cannot be converted to int by integral promotion, the program is ill-formed.

Overload (6) of std::abs for std::intmax_t is provided in <cinttypes> if and only if std::intmax_t is an extended integer type.

(since C++11)

Parameters

num

-

integer value

Return value

The absolute value of num (i.e. |num|), if it is representable.

Notes

In 2's complement systems, the absolute value of the most-negative value is out of range, e.g. for 32-bit 2's complement type int, INT_MIN is -2147483648, but the would-be result 2147483648 is greater than INT_MAX, which is 2147483647.

Example

Run this code

#include <climits>
#include <cstdlib>
#include <iostream>
 
int main()
{
    std::cout << std::showpos
              << "abs(+3) = " << std::abs(3) << '\n'
              << "abs(-3) = " << std::abs(-3) << '\n';
 
//  std::cout << std::abs(INT_MIN); // undefined behavior on 2's complement systems
}

Output:

abs(+3) = +3
abs(-3) = +3

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

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abs(float)fabsfabsffabsl (C++11)(C++11)	absolute value of a floating point value (\(\small{\|x\|}\) $\|x\|$ ) (function)
abs(std::complex)	returns the magnitude of a complex number (function template)
abs(std::valarray)	applies the function abs to each element of valarray (function template)