Q151673: FIX: Compiler Allocates Struct with Nested Struct Incorrectly

Article: Q151673
Product(s): Microsoft C Compiler
Version(s): 4.0,4.1,4.2
Operating System(s): 
Keyword(s): kbCodeGen kbVC500fix
Last Modified: 30-JUL-2001

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The information in this article applies to:

- Microsoft Visual C++, versions 4.0, 4.1, 4.2 
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SYMPTOMS
========

In the sample code below, the amount of space the compiler allocates for struct
A is incorrect. It is influenced by adding a member with data type double to the
nested struct in A even though A only declares a pointer to this nested struct
and not an instance of the struct itself. If you uncomment the line with the
double member, the code will produce different results. The size of struct A
will be reported as being larger.

Changing the size of the nested struct by adding a member of any data type other
than double does not affect the size of struct A.

RESOLUTION
==========

The problem is very specific to code similar to that below, so there are no
generic workarounds. It may be necessary to change the data type of the member
to something other than a double.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This bug was corrected in Visual C++ version 5.0.

MORE INFORMATION
================

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

     /* Compile options needed: none
     */ 

     #include <stdio.h>

     struct A
     {
         long l1;
         long l2;

         struct
         {
             int i1;
             long l3;
     //        double d1;
         } *s1;
     };

     void main()
     {
         printf( "sizeof(struct A) should be 12\n" );
         printf( "sizeof(struct A) = %d\n", sizeof(struct A) );
     }

Additional query words: kbVC400bug

======================================================================
Keywords          : kbCodeGen kbVC500fix 
Technology        : kbVCsearch kbVC400 kbAudDeveloper kbVC410 kbVC420
Version           : :4.0,4.1,4.2
Issue type        : kbbug
Solution Type     : kbfix

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