man3/getdtablesize.3

   1 .\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
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  25 .\" Modified 2002-04-15 by Roger Luethi <rl@hellgate.ch> and aeb
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  27 .TH GETDTABLESIZE 3 2016-03-15 "Linux" "Linux Programmer's Manual"
  28 .SH NAME
  29 getdtablesize \- get file descriptor table size
  30 .SH SYNOPSIS
  31 .B #include <unistd.h>
  32 .PP
  33 .B int getdtablesize(void);
  34 .PP
  35 .in -4n
  36 Feature Test Macro Requirements for glibc (see
  37 .BR feature_test_macros (7)):
  38 .in
  39 .PP
  40 .BR getdtablesize ():
  41 .ad l
  42 .RS 4
  43 .PD 0
  44 .TP 4
  45 Since glibc 2.12:
  46 .nf
  47 /* Glibc since 2.19: */ _DEFAULT_SOURCE
  48     || /* Glibc versions <= 2.19: */ _BSD_SOURCE
  49     || ! (_POSIX_C_SOURCE\ >=\ 200112L)
  50 .TP 4
  51 .fi
  52 Before glibc 2.12:
  53 _BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
  54 .\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  55 .PD
  56 .RE
  57 .ad b
  58 .SH DESCRIPTION
  59 .BR getdtablesize ()
  60 returns the maximum number of files a process can have open,
  61 one more than the largest possible value for a file descriptor.
  62 .SH RETURN VALUE
  63 The current limit on the number of open files per process.
  64 .SH ERRORS
  65 On Linux,
  66 .BR getdtablesize ()
  67 can return any of the errors described for
  68 .BR getrlimit (2);
  69 see NOTES below.
  70 .SH ATTRIBUTES
  71 For an explanation of the terms used in this section, see
  72 .BR attributes (7).
  73 .TS
  74 allbox;
  75 lb lb lb
  76 l l l.
  77 Interface       Attribute       Value
  78 T{
  79 .BR getdtablesize ()
  80 T}      Thread safety   MT-Safe
  81 .TE
  82 .SH CONFORMING TO
  83 SVr4, 4.4BSD (the
  84 .BR getdtablesize ()
  85 function first appeared in 4.2BSD).
  86 It is not specified in POSIX.1;
  87 portable applications should employ
  88 .I sysconf(_SC_OPEN_MAX)
  89 instead of this call.
  90 .SH NOTES
  91 .BR getdtablesize ()
  92 is implemented as a libc library function.
  93 The glibc version calls
  94 .BR getrlimit (2)
  95 and returns the current
  96 .B RLIMIT_NOFILE
  97 limit, or
  98 .B OPEN_MAX
  99 when that fails.
 100 .\" The libc4 and libc5 versions return
 101 .\" .B OPEN_MAX
 102 .\" (set to 256 since Linux 0.98.4).
 103 .SH SEE ALSO
 104 .BR close (2),
 105 .BR dup (2),
 106 .BR getrlimit (2),
 107 .BR open (2)