/*------------------------------------------------------------------*/
/* testtmpfile.c                                                    */
/* Demonstrate the tmpfile() function.                              */
/*------------------------------------------------------------------*/

#include <stdio.h>
#include <assert.h>

int main(void)

/* Demonstrate using the tmpfile() function to change the contents
   of a file.  The program assumes that a file named "origfile"
   exists.  Return 0.  */

{
   FILE *psOrigFile;
   FILE *psTempFile;
   int iChar;

   /* Open the original file. */
   psOrigFile = fopen("origfile", "r");
   assert(psOrigFile != NULL);

   /* Open the temporary file. */
   psTempFile = tmpfile();
   assert(psTempFile != NULL);

   /* Copy all data from the original file to the temporary file. */
   while ((iChar = getc(psOrigFile)) != EOF)
      putc(iChar, psTempFile);

   /* Write one more line to psTempFile. */
   fprintf(psTempFile, "This is another line.\n");
   
   /* Close the original file, and reopen it for writing. */
   fclose(psOrigFile);
   psOrigFile = fopen("origfile", "w");
   assert(psOrigFile != NULL);

   /* Move the temporary file's pointer to the beginning of the file. */
   fseek(psTempFile, 0, SEEK_SET);

   /* Copy all data from the temporary file back to the original file. */ 
   while ((iChar = getc(psTempFile)) != EOF)
      putc(iChar, psOrigFile);

   /* Close both files. */
   fclose(psOrigFile);
   fclose(psTempFile);

   return 0;
}


/* Sample execution:

$ gcc -Wall -ansi -pedantic -o testtmpfile testtmpfile.c
$ cat origfile
This is line one.
This is line two.
$ testtmpfile
$ cat origfile
This is line one.
This is line two.
This is another line.
*/