Namespaces
Variants

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

From cppreference.net
C++
Numerics library
Common mathematical functions
Nearest integer floating point operations
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Floating point manipulation functions
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Classification and comparison
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Types
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Macro constants
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>
(6) (since C++11)
(constexpr since C++23)
(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)

Contents

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

See also

(C++11) (C++11)
absolute value of a floating point value ( |x| )
(function)
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