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.\" Copyright (c) 1989, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)mktemp.3 8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.Dt MKTEMP 3
.Os
.Sh NAME
.Nm mktemp
.Nd make temporary file name (unique)
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft char *
.Fn mktemp "char *template"
.Ft int
.Fn mkstemp "char *template"
.Sh DESCRIPTION
The
.Fn mktemp
function
takes the given file name template and overwrites a portion of it
to create a file name.
This file name is unique and suitable for use
by the application.
The template may be any file name with some number of
.Ql X Ns s
appended
to it, for example
.Pa /tmp/temp.XXXX .
The trailing
.Ql X Ns s
are replaced with the current process number and/or a
unique letter combination.
The number of unique file names
.Fn mktemp
can return depends on the number of
.Ql X Ns s
provided; six
.Ql X Ns s
will
result in
.Fn mktemp
testing roughly 26 ** 6 combinations.
.Pp
The
.Fn 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.
.Sh RETURN VALUES
The
.Fn mktemp
function
returns a pointer to the template on success and
.Dv NULL
on failure.
The
.Fn mkstemp
function
returns \-1 if no suitable file could be created.
If either call fails an error code is placed in the global variable
.Va errno .
.Sh ERRORS
The
.Fn mktemp
and
.Fn mkstemp
functions
may set
.Va errno
to one of the following values:
.Bl -tag -width [ENOTDIR]
.It Bq Er ENOTDIR
The pathname portion of the template is not an existing directory.
.El
.Pp
The
.Fn mktemp
and
.Fn mkstemp
functions
may also set
.Va errno
to any value specified by the
.Xr stat 2
function.
.Pp
The
.Fn mkstemp
function
may also set
.Va errno
to any value specified by the
.Xr open 2
function.
.Sh NOTES
A common problem that results in a core dump is that the programmer
passes in a read-only string to
.Fn mktemp
or
.Fn mkstemp .
This is common with programs that were developed before
.St -ansiC
compilers were common.
For example, calling
.Fn mkstemp
with an argument of
.Qq /tmp/tempfile.XXXXXX
will result in a core dump due to
.Fn mkstemp
attempting to modify the string constant that was given.
If the program in question makes heavy use of that type
of function call, you do have the option of compiling the program
so that it will store string constants in a writable segment of memory.
See
.Xr gcc 1
for more information.
.Sh SEE ALSO
.Xr chmod 2 ,
.Xr getpid 2 ,
.Xr open 2 ,
.Xr stat 2
.Sh HISTORY
A
.Nm mktemp
function appeared in
.At v7 .
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