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 filename from
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 specified in
flags: O_APPEND, 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
flags argument given to mkostemp() is unnecessary, and produces errors on some systems.
The mkstemps() function is like mkstemp(), except that the string in
template 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 appropriately.
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
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