man3/abs.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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  23 .\" References consulted:
  24 .\"     Linux libc source code
  25 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  26 .\"     386BSD man pages
  27 .\" Modified Mon Mar 29 22:31:13 1993, David Metcalfe
  28 .\" Modified Sun Jun  6 23:27:50 1993, David Metcalfe
  29 .\" Modified Sat Jul 24 21:45:37 1993, Rik Faith (faith@cs.unc.edu)
  30 .\" Modified Sat Dec 16 15:02:59 2000, Joseph S. Myers
  31 .\"
  32 .TH ABS 3  2007-07-26 "GNU" "Linux Programmer's Manual"
  33 .SH NAME
  34 abs, labs, llabs, imaxabs \- compute the absolute value of an integer
  35 .SH SYNOPSIS
  36 .nf
  37 .B #include <stdlib.h>
  38 .sp
  39 .BI "int abs(int " j );
  40 .br
  41 .BI "long int labs(long int " j );
  42 .br
  43 .BI "long long int llabs(long long int " j );
  44 .sp
  45 .B #include <inttypes.h>
  46 .sp
  47 .BI "intmax_t imaxabs(intmax_t " j );
  48 .fi
  49 .sp
  50 .in -4n
  51 Feature Test Macro Requirements for glibc (see
  52 .BR feature_test_macros (7)):
  53 .in
  54 .sp
  55 .ad l
  56 .BR llabs ():
  57 .RS 4
  58 _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE;
  59 .br
  60 or
  61 .I cc\ -std=c99
  62 .ad
  63 .SH DESCRIPTION
  64 The
  65 .BR abs ()
  66 function computes the absolute value of the integer
  67 argument \fIj\fP.
  68 The
  69 .BR labs (),
  70 .BR llabs ()
  71 and
  72 .BR imaxabs ()
  73 functions compute the absolute value of the argument \fIj\fP of the
  74 appropriate integer type for the function.
  75 .SH "RETURN VALUE"
  76 Returns the absolute value of the integer argument, of the appropriate
  77 integer type for the function.
  78 .SH "CONFORMING TO"
  79 SVr4, POSIX.1-2001, 4.3BSD, C99.
  80 .\" POSIX.1 (1996 edition) only requires the
  81 .\" .BR abs ()
  82 .\" function.
  83 C89 only
  84 includes the
  85 .BR abs ()
  86 and
  87 .BR labs ()
  88 functions; the functions
  89 .BR llabs ()
  90 and
  91 .BR imaxabs ()
  92 were added in C99.
  93 .SH NOTES
  94 Trying to take the absolute value of the most negative integer
  95 is not defined.
  96 .PP
  97 The
  98 .BR llabs ()
  99 function is included in glibc since version 2.0, but
 100 is not in libc5 or libc4.
 101 The
 102 .BR imaxabs ()
 103 function is included in
 104 glibc since version 2.1.1.
 105 .PP
 106 For
 107 .BR llabs ()
 108 to be declared, it may be necessary to define
 109 \fB_ISOC99_SOURCE\fP or \fB_ISOC9X_SOURCE\fP (depending on the
 110 version of glibc) before including any standard headers.
 111 .PP
 112 GCC handles
 113 .BR abs ()
 114 and
 115 .BR labs ()
 116 as built-in functions.
 117 GCC 3.0 also handles
 118 .BR llabs ()
 119 and
 120 .BR imaxabs ()
 121 as built-ins.
 122 .SH "SEE ALSO"
 123 .BR cabs (3),
 124 .BR ceil (3),
 125 .BR fabs (3),
 126 .BR floor (3),
 127 .BR rint (3)