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

getdtablesize - get file descriptor table size

#include <unistd.h>
int getdtablesize(void);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

getdtablesize():

Since glibc 2.20:
    _DEFAULT_SOURCE || ! (_POSIX_C_SOURCE >= 200112L)
Glibc 2.12 to 2.19:
    _BSD_SOURCE || ! (_POSIX_C_SOURCE >= 200112L)
Before glibc 2.12:
    _BSD_SOURCE || _XOPEN_SOURCE >= 500

getdtablesize() returns the maximum number of files a process can have open, one more than the largest possible value for a file descriptor.

The current limit on the number of open files per process.

On Linux, getdtablesize() can return any of the errors described for getrlimit(2); see NOTES below.

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

SVr4, 4.4BSD (the getdtablesize() function first appeared in 4.2BSD). It is not specified in POSIX.1; portable applications should employ sysconf(_SC_OPEN_MAX) instead of this call.

The glibc version of getdtablesize() calls getrlimit(2) and returns the current RLIMIT_NOFILE limit, or OPEN_MAX when that fails.

close(2), dup(2), getrlimit(2), open(2)

This page is part of release 5.13 of the Linux 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/.
2021-03-22 Linux