INFO: Two Syntaxes for Calling Functions with Pointers

ID: Q32109

The information in this article applies to:

Microsoft C for MS-DOS, versions 5.1, 6.0, 6.0a, 6.0ax
Microsoft C/C++ for MS-DOS
Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5
Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 4.0, 5.0, 6.0

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)();

-or-


pointer_to_function();

The behavior exhibited in the sample code is expected. The ANSI Standard (Document Number X3J11/88-002, January 11, 1988) allows a function to be called through a pointer with the following syntax


(*pointer_to_function)();

in addition to the following non-traditional syntax:


pointer_to_function();

The text below is quoted from page 41 of the "Rationale for Draft Proposed American National Standard for Information Systems Programming Language C" (sec. 3.3.2.2, "Function calls"):

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");
}

Additional query words:

Keywords : kbLangC kbVC100 kbVC150 kbVC200 kbVC400 kbVC500 kbVC600
Version : MS-DOS:; WINDOWS:1.0,1.5; winnt:1.0,2.0,4.0,5.0,6.0
Platform : MS-DOS WINDOWS winnt
Issue type : kbinfo