tmpnam, tmpnam_s
Header: <stdio.h>
- Creates a unique valid file name (no longer than L_tmpnam in length) and stores it in character string pointed to by filename. The function is capable of generating up to TMP_MAX of unique filenames, but some or all of them may be in use in the filesystem and thus not suitable return values.
# Declarations
char *tmpnam( char *filename );
errno_t tmpnam_s(char *filename_s, rsize_t maxsize);
(since C11)
#define TMP_MAX /*unspecified*/
#define TMP_MAX_S /*unspecified*/
(since C11)
#define L_tmpnam /*unspecified*/
#define L_tmpnam_s /*unspecified*/
(since C11)
# Parameters
filename: pointer to the character array capable of holding at least L_tmpnam bytes, to be used as a result buffer. If null pointer is passed, a pointer to an internal static buffer is returned.filename_s: pointer to the character array capable of holding at least L_tmpnam_s bytes, to be used as a result buffer.maxsize: maximum number of characters the function is allowed to write (typically the size of the filename_s array).
# Notes
Although the names generated by tmpnam are difficult to guess, it is possible that a file with that name is created by another process between the moment tmpnam returns and the moment this program attempts to use the returned name to create a file. The standard function tmpfile and the POSIX function mkstemp do not have this problem (creating a unique directory using only the standard C library still requires the use of tmpnam).
POSIX systems additionally define the similarly named function tempnam, which offers the choice of a directory (which defaults to the optionally defined macro P_tmpdir).
# Example
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(void)
{
// Note, the compiler/linker may issue a security warning, e.g. GCC:
// "warning: the use of `tmpnam' is dangerous, better use `mkstemp'"
char* name1 = tmpnam(NULL);
printf("temporary file name: %s\n", name1);
char name2[L_tmpnam];
if (tmpnam(name2))
printf("temporary file name: %s\n", name2);
// POSIX offers mkstemp. The following declaration might be
// necessary as mkstemp is absent in the standard C <stdlib.h>.
int mkstemp(char*);
char name3[] = "/tmp/fileXXXXXX"; // at least six 'X' required ^_^
int file_descriptor = mkstemp(name3);
if (file_descriptor != -1)
printf("temporary file name: %s\n", name3);
else
perror("mkstemp");
}