.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
.\" Modified 2002-04-15 by Roger Luethi <rl@hellgate.ch> and aeb
.\"
.TH GETDTABLESIZE 3 2016-03-15 "Linux" "Linux Programmer's Manual"
.SH NAME
getdtablesize \- get file descriptor table size
.SH SYNOPSIS
.B #include <unistd.h>
.sp
.B int getdtablesize(void);
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR getdtablesize ():
.ad l
.RS 4
.PD 0
.TP 4
Since glibc 2.12:
.nf
/* Glibc since 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE
    || ! (_POSIX_C_SOURCE\ >=\ 200112L)
.TP 4
.fi
Before glibc 2.12:
_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
.\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
.PD
.RE
.ad b
.SH DESCRIPTION
.BR getdtablesize ()
returns the maximum number of files a process can have open,
one more than the largest possible value for a file descriptor.
.SH RETURN VALUE
The current limit on the number of open files per process.
.SH ERRORS
On Linux,
.BR getdtablesize ()
can return any of the errors described for
.BR getrlimit (2);
see NOTES below.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lb lb lb
l l l.
Interface	Attribute	Value
T{
.BR getdtablesize ()
T}	Thread safety	MT-Safe
.TE
.SH CONFORMING TO
SVr4, 4.4BSD (the
.BR getdtablesize ()
function first appeared in 4.2BSD).
It is not specified in POSIX.1;
portable applications should employ
.I sysconf(_SC_OPEN_MAX)
instead of this call.
.SH NOTES
.BR getdtablesize ()
is implemented as a libc library function.
The glibc version calls
.BR getrlimit (2)
and returns the current
.B RLIMIT_NOFILE
limit, or
.B OPEN_MAX
when that fails.
.\" The libc4 and libc5 versions return
.\" .B OPEN_MAX
.\" (set to 256 since Linux 0.98.4).
.SH SEE ALSO
.BR close (2),
.BR dup (2),
.BR getrlimit (2),
.BR open (2)
.SH COLOPHON
This page is part of release 4.10 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.