Q63058: Function Prototype with Undefined Structure Causes Error

Article: Q63058
Product(s): See article
Version(s): 6.00   | 6.00
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | | mspl13_c
Last Modified: 25-JUL-1990

A function prototype, which is defined using an undeclared structure
in C version 6.00, will give the following error message:

   error C2079: 'Formal' uses undefined struct/union '<union name>'

In C 5.10, the same program (assuming the structure is defined
sometime before the function itself is defined) will compile without
any errors or warnings.

Sample Code
-----------

#include "stdio.h"

// prototype

void ItFunc(struct s);

// the struct itself

struct s
{
   int x;
   int y;
};

void ItFunc(xstruct)
struct s xstruct;
{
  printf("in the function\n");
}

For this code to compile correctly in C 6.00, the structure definition
should appear before the function prototype.

Microsoft is researching this problem and will post new information
here as it becomes available.

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.