FIX: MIDL compiler structure packing problems

MORE INFORMATION

Fully interpreted stubs (MIDL option /Oi) use another approach for parameter marshaling, and this alternative approach does not have the problem with the packing. The stub code produced with /Oi is slightly slower, but for most applications the loss is negligible. If you decide to use the /Oi option, make sure your remote procedures are declared as __stdcall. Refer to the MIDL documentation for more information on /Oi.

If you are not interested in using the /Oi option, you can manually pad your interface declaration. To manually pad your interface declaration, you must first determine the packing used by the C compiler. Visual C++ 2.x for the x86 uses a packing of 4 by default. Otherwise, the packing is specified by /Zp or #pramga pack(). Each element must start on a multiple of the packing size.

The following example shows how to pad a structure with a packing of 4.

   typedef struct   // This struct goes in the C code
   {
      char c;
      long l;
   } PADDED_BY_COMPILER_STRUCT;

   typedef struct   // This struct goes in the IDL file
   {
      char c;
      char pad[3];  // Add 3 bytes to align the next field on byte 4
      long l;
   } MANUALLY_PADDED_IDL_STRUCT;
				

Another alternative is to wrap the stub code generated by MIDL with

   #pragma pack(1)
				

Each time MIDL generates the stub code, you must insert #pragma pack statements into the server stub.

For example:

   /* File created by MIDL compiler version 2.00.0102 */ 
   /* at Fri Aug 18 13:48:23 1995
    */ 
   //@@MIDL_FILE_HEADING(  )

   #pragma pack(1)         // Added to fix MIDL pack problem

   #include <string.h>
   #include "bug.h"

   ... code generated by MIDL ...

   #pragma pack()          // Added to revert to default packing