tmpnam, tmpnam_s

tmpnam and tmpnam_s modify static state (which may be shared between these functions) and are not required to be thread-safe.

Parameters

Return value

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");
}

temporary file name: /tmp/file90dLlR
temporary file name: /tmp/fileY9LWAg
temporary file name: /tmp/filexgv8PF

References

See also