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ABS(3) Linux Programmer's Manual ABS(3)

abs, labs, llabs, imaxabs - compute the absolute value of an integer

#include <stdlib.h>
int abs(int j);
long int labs(long int j);
long long int llabs(long long int j);
#include <inttypes.h>
intmax_t imaxabs(intmax_t j);


Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

llabs():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

The abs() function computes the absolute value of the integer argument j. The labs(), llabs() and imaxabs() functions compute the absolute value of the argument j of the appropriate integer type for the function.

Returns the absolute value of the integer argument, of the appropriate integer type for the function.

For an explanation of the terms used in this section, see attributes(7).
Interface Attribute Value
abs (), labs (), llabs (), imaxabs () Thread safety MT-Safe

POSIX.1-2001, POSIX.1-2008, C99, SVr4, 4.3BSD. C89 only includes the abs() and labs() functions; the functions llabs() and imaxabs() were added in C99.

Trying to take the absolute value of the most negative integer is not defined.

The llabs() function is included in glibc since version 2.0. The imaxabs() function is included in glibc since version 2.1.1.

For llabs() to be declared, it may be necessary to define _ISOC99_SOURCE or _ISOC9X_SOURCE (depending on the version of glibc) before including any standard headers.

By default, GCC handles abs(), labs(), and (since GCC 3.0) llabs() and imaxabs() as built-in functions.

cabs(3), ceil(3), fabs(3), floor(3), rint(3)

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2016-03-15 GNU