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.\"     @(#)mktemp.3	8.1 (Berkeley) 6/4/93
.\"
.TH MKTEMP 3 "27 January 1997" GNO "Library Routines"
.SH NAME
.BR mktemp
\- make temporary file name (unique)
.SH SYNOPSIS
#include <unistd.h>
.sp 1
char *
\fBmktemp\fR (char *\fItemplate\fR);
.br
int
\fBmkstemp\fR (char *\fItemplate\fR);
.SH DESCRIPTION
The
.BR 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
.IR X \'s
appended
to it, for example \fB/tmp/temp.\fIXXXX\fR.
The trailing
.IR X \'s
are replaced with the current process number and/or a
unique letter combination.
The number of unique file names
.BR mktemp 
can return depends on the number of
.IR X \'s
provided; six
.IR X \'s
will
result in
.BR mktemp 
testing roughly 26 ** 6 combinations.
.LP
The
.BR 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
.BR mktemp 
function
returns a pointer to the template on success and
.BR NULL
on failure.
The
.BR mkstemp 
function
returns \-1 if no suitable file could be created.
If either call fails an error code is placed in the global variable
.IR errno .
.SH ERRORS
The
.BR mktemp 
and
.BR mkstemp 
functions
may set
.IR errno
to one of the following values:
.RS
.IP \fBENOTDIR\fR
The pathname portion of the template is not an existing directory.
.RE
.LP
The
.BR mktemp 
and
.BR mkstemp 
functions
may also set
.IR errno
to any value specified by the
.BR stat (2)
function.
.LP
The
.BR mkstemp 
function
may also set
.IR errno
to any value specified by the
.BR open (2)
function.
.SH NOTES
A common problem that results in a core dump on many architectures
is that the programmer passes in a read-only string to 
.BR mktemp 
or 
.BR mkstemp .
This is common with programs that were developed before 
ANSI/C compilers were common.
For example, calling
.BR mkstemp 
with an argument of \fB/tmp/tempfile.\fIXXXXXX\fR
will result in a core dump due to 
.BR mkstemp 
attempting to modify the string constant that was given.
If the program in question makes heavy use of that type
of function call, some compilers have the option of compiling the program
so that it will store string constants in a writable segment of memory
(in the data rather than the text segment).  While it is good programming
practise to avoid this problem, it is not strictly necessary under GNO
due to the lack of a write-only text segment.
.SH SEE ALSO
.BR chmod (2),
.BR getpid (2),
.BR open (2),
.BR stat (2)
.SH HISTORY
A
.BR mktemp
function appeared in Version 7 AT&T UNIX.