Does VB6 have a #pragma pack equivalent?

Question

I am developing a TCP/IP client that has to deal with a proprietary binary protocol. I was considering using user-defined types to represent the protocol headers, and using CopyMemory to shuffle data to and from the UDT and a byte array. However, it appears that VB6 adds padding bytes to align user-defined types. Is there any way to force VB6 to not pad UDT's, similar to the #pragma pack directive available in many C/C++ compilers? Perhaps a special switch passed to the compiler?

Answer 1

No.

Your best best is to write the low level stuff in C or C++ (where you do have #pragma pack), then expose the interface via COM.

(Out of curiosity, why are you still working with VB6 instead of VB.NET?)

Answer 2

There is not any way to force VB6 to not pad UDT's, similar to the #pragma pack directive available in many C/C++ compilers, but you can do it the other way around.

According to Q194609 Visual Basic uses 4 bytes alignment and Visual C++ uses 8 bytes by default.

When using VB6 to call out to a C DLL, I used the MS "pshpack4.h" header files to handle the alignment because various compilers do this in different ways, as shown in this (rather edited) example:

// this is in a header file called vbstruct.h
...

# define VBSTRING     char
# define VBFIXEDSTRING  char
# define VBDATE      double
# define VBSINGLE    float

# ifdef _WIN32
#  define VBLONG     long
#  define VBINT      short
# else  // and this was for 16bit code not 64bit!!!!
#  define VBLONG     long
#  define VBINT      int
# endif
...

#  include "pshpack4.h"
...

typedef struct  VbComputerNameStruct
    {
    VBLONG           sName;
    VBSTRING         ComputerName[VB_COMPUTERNAME_LENGTH];
    }           VbComputerNameType;


typedef struct  VbNetwareLoginInfoStruct
    {
    VBLONG            ObjectId;
    VBINT            ObjectType;
    VBSTRING          ObjectName[48];
    }           VbNetwareLoginInfoType;
...

#  include "poppack.h"