INFO: Two Syntaxes for Calling Functions with Pointers

• Microsoft C for MS-DOS, versions 5.1, 6.0, 6.0a, 6.0ax
• Microsoft C/C++ for MS-DOS, version 7.0
• Microsoft Visual C++ for Windows, versions 1.0, 1.5
• Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.0, 4.0, 5.0

SUMMARY

The source code below contains what appears to be an improper use of a pointer to a function. However, the code is correct. There are two ways to call a function when using a pointer to a function:

   (*pointer_to_function)();

   pointer_to_function();

   (*pointer_to_function)();

   pointer_to_function();

   The latter construct, not sanctioned in the Base Document, appears
   in some present versions of C, is unambiguous, invalidates no old
   code, and can be an important shorthand.

MORE INFORMATION

The sample code below demonstrates this method.

Sample Code

   /*
    * Compile options needed: none
    */

   #include <stdio.h>

   void main(void)
   {
      void ftn(void);
      void (*ptr_to_ftn)(void);

      ptr_to_ftn = ftn;   // The pointer is correctly assigned
                          // the address of 'ftn()'

      printf("\nCalling the function\n\n");

      (ptr_to_ftn)();     // This is not traditional syntax for
                          // a call through a function pointer

      printf("back to main\n");
   }

   void ftn(void)
   {
      printf("in the function\n\n");
   }

Keywords          : CLngIss kbfasttip
Version           : MS-DOS:5.1,6.0,6.00a,6.00ax,7.0; WINDOWS:1.0,1.5; WINDOWS  NT:1.0,2.0,4.0,5.0
Platform          : MS-DOS NT WINDOWS
Issue type        : kbinfo