mkdtemp man page

Prolog

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

mkdtemp, mkstemp — create a unique directory or file

Synopsis

#include <stdlib.h>

char *mkdtemp(char *template);
int mkstemp(char *template);

Description

The mkdtemp() function uses the contents of template to construct a unique directory name. The string provided in template shall be a pathname ending with six trailing 'X's. The mkdtemp() function shall replace each 'X' with a character from the portable filename character set. The characters are chosen such that the resulting name does not duplicate the name of an existing file at the time of a call to mkdtemp(). The unique directory name is used to attempt to create the directory using mode 0700 as modified by the file creation mask.

The mkstemp() function shall replace the contents of the string pointed to by template by a unique pathname, and return a file descriptor for the file open for reading and writing. The mkstemp() function shall create the file, and obtain a file descriptor for it, as if by a call to:

open(pathname, O_RDWR|O_CREAT|O_EXCL, S_IRUSR|S_IWUSR)

The function thus prevents any possible race condition between testing whether the file exists and opening it for use. The string in template should look like a pathname with six trailing 'X's; mkstemp() replaces each 'X' with a character from the portable filename character set. The characters are chosen such that the resulting name does not duplicate the name of an existing file at the time of a call to mkstemp().

Return Value

Upon successful completion, the mkdtemp() function shall return a pointer to the string containing the directory name if it was created. Otherwise, it shall return a null pointer and shall set errno to indicate the error.

Upon successful completion, the mkstemp() function shall return an open file descriptor. Otherwise, it shall return -1 if no suitable file could be created.

Errors

The mkdtemp() function shall fail if:

EACCES
Search permission is denied on a component of the path prefix, or write permission is denied on the parent directory of the directory to be created.
EINVAL
The string pointed to by template does not end in "XXXXXX".
ELOOP
A loop exists in symbolic links encountered during resolution of the path of the directory to be created.
EMLINK
The link count of the parent directory would exceed {LINK_MAX}.
ENAMETOOLONG
The length of a component of a pathname is longer than {NAME_MAX}.
ENOENT
A component of the path prefix specified by the template argument does not name an existing directory.
ENOSPC
The file system does not contain enough space to hold the contents of the new directory or to extend the parent directory of the new directory.
ENOTDIR
A component of the path prefix names an existing file that is neither a directory nor a symbolic link to a directory.
EROFS
The parent directory resides on a read-only file system.

The mkdtemp() function may fail if:

ELOOP
More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path of the directory to be created.
ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname resolution of a symbolic link produced an intermediate result with a length that exceeds {PATH_MAX}.

The error conditions for the mkstemp() function are defined in open().

The following sections are informative.

Examples

Generating a Pathname

The following example creates a file with a 10-character name beginning with the characters "file" and opens the file for reading and writing. The value returned as the value of fd is a file descriptor that identifies the file.

#include <stdlib.h>
...
char template[] = "/tmp/fileXXXXXX";
int fd;

fd = mkstemp(template);

Application Usage

It is possible to run out of letters.

The mkdtemp() and mkstemp() functions need not check to determine whether the filename part of template exceeds the maximum allowable filename length.

See Also

getpid(), mkdir(), open(), tmpfile(), tmpnam()

The Base Definitions volume of POSIX.1‐2008, <stdlib.h>

Info

2013 IEEE/The Open Group POSIX Programmer's Manual