INFO: Function Pointers to Functions with Different Parameters

• Microsoft C for MS-DOS, versions 6.0, 6.0a, 6.0ax
• Microsoft C for OS/2, versions 6.0, 6.0a
• 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 sample code below illustrates how to use function pointers to call functions that take different parameters than those with which the pointer was declared. The function is cast to the type of the function pointer during the first assignment, then the function pointer is cast to the type of the function to be called. Using typedefs generally makes it easier than casting the pointer directly.

Sample Code

   /* Compile options needed: none
   */

   #include <stdio.h>

   typedef int  (*myintchartype) (char *, char *);
   typedef void (*myvoidtype) (void);
   typedef int  (*myintvoidtype) (void);

   int func1(char *, char *);
   void func2(void);

   void main(void)
   {
      myintvoidtype ptr;

      ptr = (myintvoidtype) func1;
      ((myintchartype) ptr)("one", "two");

      ptr = (myintvoidtype) func2;
      ((myvoidtype) ptr)();
   }

   int func1(char *a, char *b)
   {
      return printf("func1 took two parameters: %s and %s\n", a, b);
   }

   void func2(void)
   {
      printf("func2 did not take any parameters\n");
   }