@node tmpnam, stdio
@findex tmpnam
@vindex TMPDIR@r{ environment variable, and }tmpnam
@vindex TEMP@r{ environment variable, and }tmpnam
@vindex TMP@r{ environment variable, and }tmpnam
@subheading Syntax

@example
#include <stdio.h>

char *tmpnam(char *s);
@end example

@subheading Description

This function generates a string that is a valid file name and that
is not the same as the name of an existing file.  A different string is
guaranteed to be produced each time it is called, up to @code{TMP_MAX}
times (@code{TMP_MAX} is defined on stdio.h).  If @code{tmpnam} is called
more than TMP_MAX times, the behavior is implementation-dependent (ours
just wraps around and tries to reuse the same file names from the
beginning).

This function examines the environment to determine the directory in which
the temporary file will be opened.  It looks for one of the variables
@code{"TMPDIR"}, @code{"TEMP"} and @code{"TMP"}, in that order.  The first
one which is found in the environment will be used on the assumption that
it points to a directory.  If neither of the above variables is defined,
@code{tmpnam} defaults to the "c:/" directory (which under MS-DOS might
mean that it fails to generate TMP_MAX unique names, because DOS root
directories cannot grow beyond certain limits).

@subheading Return Value

If @var{s} is a null pointer, @code{tmpnam} leaves its result in an
internal static buffer and returns a pointer to that buffer.  If @var{s}
is not a null pointer, it is assumed to point to an array of at least
@code{L_tmpnam} characters, and @code{tmpnam} writes its result in that
array and returns a pointer to it as its value.

@subheading Portability

@portability ansi, posix

@subheading Example

@example
char buf[L_tmpnam];
char *s = tmpnam(buf);
@end example