mkdtemp

Synopsis

#include <stdlib.h>

char *mkdtemp(char *template);

int mkstemp(char *template);

Status

Implemented

Conformance

IEEE Std 1003.1-2017

Description

The mkdtemp() function shall create a directory with a unique name derived from template. The application shall ensure that the string provided in template is a path name ending with at least six trailing 'X' characters. The mkdtemp() function shall modify the contents of template by replacing six or more 'X' characters at the end of the path name with the same number of characters from the portable filename character set. The characters shall be chosen such that the resulting path name does not duplicate the name of an existing file at the time of the call to mkdtemp(). The mkdtemp() function shall use the resulting path name to create the new directory as if by a call to:

mkdir(pathname, S_IRWXU)

The mkstemp() function shall create a regular file with a unique name derived from template and return a file descriptor for the file open for reading and writing. The application shall ensure that the string provided in template is a path name ending with at least six trailing 'X' characters. The mkstemp() function shall modify the contents of template by replacing six or more 'X' characters at the end of the path name with the same number of characters from the portable filename character set. The characters shall be chosen such that the resulting path name does not duplicate the name of an existing file at the time of the call to mkstemp(). The mkstemp() function shall use the resulting path name to 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)

By behaving as if the O_EXCL flag for open() is set, the function prevents any possible race condition between testing whether the file exists and opening it for use.

Exactly the last six 'X' characters are replaced with characters chosen at random; any additional trailing 'X' characters are treated as a fixed part of the template.

Return value

Upon successful completion, the mkdtemp() function shall return the value of template. 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 and shall set errno to indicate the error.

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 path name is longer than {NAME_MAX} (see POSIX deviations).

  • 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 path name exceeds {PATH_MAX}, or path name 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().

POSIX deviations

The length of a path name component is not checked against NAME_MAX by libphoenix (except for the name of the directory created by mkdtemp()), but by the filesystem server, against the name length limit of the filesystem, which may differ from NAME_MAX. The error reported for a too long component of the path prefix, or of the name of the file created by mkstemp(), therefore depends on the filesystem (see the deviations of open()). Checking every component in libphoenix would require knowing the name length limit of every mounted filesystem in each process, so the check is left to the filesystem server, which knows its own limit.