mktemp3

Usage

Library

Standard C Library (libc, -lc)

Overview

The mktemp() function takes the given file name template and overwrites a portion of it to create a file name. This file name is guaranteed not to exist at the time of function invocation and is suitable for use by the application. The template may be any file name with some number of ‘Xs’ appended to it, for example /tmp/temp.XXXXXX. The trailing ‘Xs’ are replaced with a unique alphanumeric combination. The number of unique file names mktemp() can return depends on the number of ‘Xs’ provided; six ‘Xs’ will result in mktemp() selecting one of 56800235584 (62 ** 6) possible temporary file names.

The mkstemp() function makes the same replacement to the template and creates the template file, mode 0600, returning a file descriptor opened for reading and writing. This avoids the race between testing for a file's existence and opening it for use.

The mkdtemp() function makes the same replacement to the template as in mktemp() and creates the template directory, mode 0700.

The mkostemp() function is like mkstemp() but allows specifying additional open(2) flags (defined in ⟨fcntl.h⟩). The permitted flags are O_APPEND, O_SHLOCK, O_EXLOCK and O_CLOEXEC.

The mkstemps() and mkostemps() functions act the same as mkstemp() and mkostemp() respectively, except they permit a suffix to exist in the template. The template should be of the form /tmp/tmpXXXXXXsuffix. The mkstemps() and mkostemps() functions are told the length of the suffix string.

The mkdtempat_np(), mkstempsat_np(), and mkostempsat_np() functions act the same as mkdtemp(), mkstemps(), and mkostemps() respectively, except in the case where the path specifies a relative path. In this case, path is treated as relative to the directory associated with the file descriptor fd instead of the current working directory.

Return values

The mktemp() and mkdtemp() functions return a pointer to the template on success and NULL on failure. The mkstemp(), mkostemp(), mkstemps() and mkostemps() functions return -1 if no suitable file could be created. If either call fails an error code is placed in the global variable errno.

Errors

The mkstemp(), mkostemp(), mkstemps(), mkostemps(), and mkdtemp() functions may set errno to one of the following values:

[ENOTDIR]

The pathname portion of the template is not an existing directory.

The mkostemp() and mkostemps() functions may also set errno to the following value:

[EINVAL]

The oflags argument is invalid.

The mkstemp(), mkostemp(), mkstemps(), mkostemps() and mkdtemp() functions may also set errno to any value specified by the stat(2) function.

The mkstemp(), mkostemp(), mkstemps() and mkostemps() functions may also set errno to any value specified by the open(2) function.

The mkdtemp() function may also set errno to any value specified by the mkdir(2) function.

Notes

A common problem that results in a core dump is that the programmer passes in a read-only string to mktemp(), mkstemp(), mkstemps() or mkdtemp(). This is common with programs that were developed before ISO/IEC 9899:1990 (“ISO C90”) compilers were common. For example, calling mkstemp() with an argument of "/tmp/tempfile.XXXXXX" will result in a core dump due to mkstemp() attempting to modify the string constant that was given.

Legacy synopsis

#include <unistd.h>

The include file ⟨unistd.h⟩ is necessary and sufficient for all functions.