mkstemp, mkostemp, mkstemps, mkostemps - create a unique temporary file
#include <stdlib.h> int mkstemp(char *template); int mkostemp(char *template, int flags); int mkstemps(char *template, int suffixlen); int mkostemps(char *template, int suffixlen, int flags);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_XOPEN_SOURCE >= 500 || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
The mkstemp() function generates a unique temporary
template, creates and opens the file, and returns
an open file descriptor for the file.
The last six characters of
template must be "XXXXXX" and
these are replaced with a string that makes the filename unique. Since
it will be modified,
template must not be a string constant,
but should be declared as a character array.
The file is created with permissions 0600, that is, read plus write for owner only. The returned file descriptor provides both read and write access to the file. The file is opened with the open(2) O_EXCL flag, guaranteeing that the caller is the process that creates the file.
The mkostemp() function is like
mkstemp(), with the difference that the following
bits—with the same meaning as for open(2)—may be
O_CLOEXEC, and O_SYNC. Note that when
creating the file, mkostemp() includes the values
O_RDWR, O_CREAT, and
O_EXCL in the
flags argument given to
open(2); including these values in the
argument given to mkostemp() is unnecessary, and
produces errors on some systems.
The mkstemps() function is like
mkstemp(), except that the string in
contains a suffix of
suffixlen characters. Thus,
template is of the form
prefixXXXXXXsuffix, and the
string XXXXXX is modified as for mkstemp().
On success, these functions return the file descriptor of the
temporary file. On error, -1 is returned, and
errno is set
Could not create a unique temporary filename. Now the contents of
template are undefined.
These functions may also fail with any of the errors described for open(2).
In glibc versions 2.06 and earlier, the file is created with permissions 0666, that is, read and write for all users. This old behavior may be a security risk, especially since other UNIX flavors use 0600, and somebody might overlook this detail when porting programs. POSIX.1-2008 adds a requirement that the file be created with mode 0600.
More generally, the POSIX specification of mkstemp() does not say anything about file modes, so the application should make sure its file mode creation mask (see umask(2)) is set appropriately before calling mkstemp() (and mkostemp()).
This page is part of release 5.10 of the Linux
project. A description of the project, information about reporting bugs,
and the latest version of this page, can be found at