man3/getdtablesize.3

   1 .\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
   2 .\"
   3 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   4 .\"
   5 .\" Modified 2002-04-15 by Roger Luethi <rl@hellgate.ch> and aeb
   6 .\"
   7 .TH getdtablesize 3 (date) "Linux man-pages (unreleased)"
   8 .SH NAME
   9 getdtablesize \- get file descriptor table size
  10 .SH LIBRARY
  11 Standard C library
  12 .RI ( libc ", " \-lc )
  13 .SH SYNOPSIS
  14 .nf
  15 .B #include <unistd.h>
  16 .PP
  17 .B int getdtablesize(void);
  18 .fi
  19 .PP
  20 .RS -4
  21 Feature Test Macro Requirements for glibc (see
  22 .BR feature_test_macros (7)):
  23 .RE
  24 .PP
  25 .BR getdtablesize ():
  26 .nf
  27     Since glibc 2.20:
  28         _DEFAULT_SOURCE || ! (_POSIX_C_SOURCE >= 200112L)
  29     Glibc 2.12 to 2.19:
  30         _BSD_SOURCE || ! (_POSIX_C_SOURCE >= 200112L)
  31     Before glibc 2.12:
  32         _BSD_SOURCE || _XOPEN_SOURCE >= 500
  33 .\"        || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
  34 .fi
  35 .SH DESCRIPTION
  36 .BR getdtablesize ()
  37 returns the maximum number of files a process can have open,
  38 one more than the largest possible value for a file descriptor.
  39 .SH RETURN VALUE
  40 The current limit on the number of open files per process.
  41 .SH ERRORS
  42 On Linux,
  43 .BR getdtablesize ()
  44 can return any of the errors described for
  45 .BR getrlimit (2);
  46 see NOTES below.
  47 .SH ATTRIBUTES
  48 For an explanation of the terms used in this section, see
  49 .BR attributes (7).
  50 .ad l
  51 .nh
  52 .TS
  53 allbox;
  54 lbx lb lb
  55 l l l.
  56 Interface       Attribute       Value
  57 T{
  58 .BR getdtablesize ()
  59 T}      Thread safety   MT-Safe
  60 .TE
  61 .hy
  62 .ad
  63 .sp 1
  64 .SH STANDARDS
  65 SVr4, 4.4BSD (the
  66 .BR getdtablesize ()
  67 function first appeared in 4.2BSD).
  68 It is not specified in POSIX.1;
  69 portable applications should employ
  70 .I sysconf(_SC_OPEN_MAX)
  71 instead of this call.
  72 .SH NOTES
  73 The glibc version of
  74 .BR getdtablesize ()
  75 calls
  76 .BR getrlimit (2)
  77 and returns the current
  78 .B RLIMIT_NOFILE
  79 limit, or
  80 .B OPEN_MAX
  81 when that fails.
  82 .\" The libc4 and libc5 versions return
  83 .\" .B OPEN_MAX
  84 .\" (set to 256 since Linux 0.98.4).
  85 .SH SEE ALSO
  86 .BR close (2),
  87 .BR dup (2),
  88 .BR getrlimit (2),
  89 .BR open (2)