Header File 

stdio.h  

Category 

Input/output Routines 

Prototype 

char *_tempnam(char *dir, char *prefix) 

wchar_t *_wtempnam(wchar_t *dir, wchar_t *prefix) 

Description 

Creates a unique file name in specified directory. 

The _tempnam function accepts single-byte or multibyte string arguments. 

The _tempnam function creates a unique file name in arbitrary directories. The unique file is not actually created; _tempnam only verifies that it does not currently exist. It attempts to use the following directories, in the order shown, when creating the file name:

• The directory specified by the TMP environment variable.
• The dir argument to _tempnam.
• The P_tmpdir definition in stdio.h. If you edit stdio.h and change this definition, _tempnam will not use the new definition.
• The current working directory.

The prefix argument specifies the first part of the file name; it cannot be longer than 5 characters, and cannot contain a period (.). A unique file name is created by concatenating the directory name, the prefix, and 6 unique characters. Space for the resulting file name is allocated with malloc; when this file name is no longer needed, the caller should call free to free it. 

If you do create a temporary file using the name constructed by _tempnam, it is your responsibility to delete the file name (for example, with a call to remove). It is not deleted automatically. (tmpfile does delete the file name.) 

Return Value 

If _tempnam is successful, it returns a pointer to the unique temporary file name, which the caller can pass to free when it is no longer needed. Otherwise, if _tempnam cannot create a unique file name, it returns NULL. 

Example  

#include <stdio.h>
#include <stdlib.h>
void main(void)
{
  FILE *stream;
  int i;
  char *name;
  for (i = 1; i <= 10; i++) {
    if ((name = tempnam("\\tmp","wow")) == NULL)
      perror("tempnam couldn't create name");
    else {
      printf("Creating %s\n",name);
      if ((stream = fopen(name,"wb")) == NULL)
        perror("Could not open temporary file\n");
      else
        fclose(stream);
    }
    free(name);
  }
  printf("Warning: temp files not deleted.\n");
}

Portability