tmpnam() — Produce temporary file name
Standards
| Standards / Extensions | C or C++ | Dependencies |
|---|---|---|
ISO C |
both |
Format
#include <stdio.h>
char *tmpnam(char *string);General description
Produces a valid file name that is not the same as the name of any existing file. It stores this name in string. If string is a NULL pointer, tmpnam() leaves the result in an internal static buffer. Any subsequent calls may modify this object. If string is not a NULL pointer, it must point to an array of at least L_tmpnam bytes. The value of L_tmpnam is defined in the stdio.h header file.
Returned value
If string is a NULL pointer, tmpnam() returns the pointer to the internal static object in which the generated unique name is placed. Otherwise, if string is not a NULL pointer, it returns the value of string. The tmpnam() function produces a different name each time it is called within a module up to at least TMP_MAX names. Files created using names returned by tmpnam() are not automatically discarded at the end of the program.
Returned value for POSIX C
The tmpnam() function behaves differently when a program is running with POSIX(ON).
When the __POSIX_TMPNAM environment variable is unset or is not set to NO, the file name returned is a unique file name in the UNIX file system. The directory component of the file name will be the value of the TMPDIR environment variable, or '/tmp' if TMPDIR is not defined.
When the __POSIX_TMPNAM environment variable is set to NO, the file name returned is as if the calling application were running POSIX(OFF).
Example
/* CELEBT14
This example calls &tmpnam. to produce a valid file name.
*/
#include <stdio.h>
int main(void)
{
char *name1;
if ((name1 = tmpnam(NULL)) !=NULL)
printf("%s can be used as a file name.\n", name1);
else printf("Cannot create a unique file name\n");
}