Q37625

layout	title	permalink
page	Q37625: MKTEMP() Function Example Clarification	/pubs/pc/reference/microsoft/kb/Q37625/

Q37625: MKTEMP() Function Example Clarification

Article: Q37625
Version(s): 5.10   | 5.10
Operating System: MS-DOS | OS/2
Flags: ENDUSER | s_quickc
Last Modified: 14-NOV-1988

The mktemp() function example in the "Microsoft C Optimizing Compiler
Run-Time Library Reference" manual is correct. However, it is not
clear that the following code statements are required:

   strcpy (names[i], template) ;
   result = mktemp(names[i]) ;

These statements ensure that mktemp() is given the original template
for each successive call. In the example, the template is defined
as "fnXXXXXX". The first call to mktemp() will produce a file
name of "fn000001". If you submit such a filename instead of
the template, "fnXXXXXX", mktemp() will fail because it is unable
to generate another unique name.

The following example demonstrates this behavior:

/*****************************************************************/
/* This is the mktemp example in the "Microsoft QuickC Run-Time  */
/* Library Reference" manual on Page 433. The example copies the */
/* template to temporary storage so as not to destroy the        */
/* original template.                                            */
/*****************************************************************/

#include <io.h>
#include <stdio.h>

char *template = "fnXXXXXX";
char *result;
char names[5][9];

main()
{
    int i;

    for (i=0;i<5;i++) {
        strcpy(names[i], template);      /* Save the template...   */
        result = mktemp(template);       /* Get another file name. */
        if (result == NULL)
            printf("Problem creating the tempfile");
        else{
            printf("the unique file name is %s\n",result);
            fopen(result, "w");
            }
                       }
)

Without the two commented lines in this example, this code fragment
generates one unique name, then terminates as the pointer "result"
becomes NULL because mktemp() cannot generate another unique name with
the template given.