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)


num - integer value

Return value

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


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.


#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


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

See also

absolute value of a floating point value (\(\small{|x|}\)|x|)
returns the magnitude of a complex number
(function template)
applies the function abs to each element of valarray
(function template)
C documentation for abs, labs, llabs

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