NetBSD/lib/libc/stdio/mktemp.3

.\"	$NetBSD: mktemp.3,v 1.8 1997/11/14 02:04:50 mrg Exp $
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.\"     @(#)mktemp.3	8.1 (Berkeley) 6/4/93
.\"
.Dd March 24, 1997
.Dt MKTEMP 3
.Os
.Sh NAME
.Nm mktemp ,
.Nm mkstemp
.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 Er
.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 SEE ALSO
.Xr chmod 2 ,
.Xr getpid 2 ,
.Xr open 2 ,
.Xr stat 2
.Sh HISTORY
A
.Fn mktemp
function appeared in
.At v7 .
.Sh BUGS
The use of
.Fn mktemp
should generally be avoided, as a hostile process can exploit a race
condition in the time between the generation of a temporary filename by
.Fn mktemp
and the invoker's use of the temporary name.
A link-time warning will be issued to advise the use of
.Fn mkstemp
instead.