Reusing Legacy DLLs in C#

// legacy.cpp : Defines the initialization routines for the DLL.
//
#include "stdafx.h"
#include "legacy.h"
#include "extlegacy.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif

//
//	Note!
//
//		If this DLL is dynamically linked against the MFC
//		DLLs, any functions exported from this DLL which
//		call into MFC must have the AFX_MANAGE_STATE macro
//		added at the very beginning of the function.
//
//		For example:
//
//		extern "C" BOOL PASCAL EXPORT ExportedFunction()
//		{
//			AFX_MANAGE_STATE(AfxGetStaticModuleState());
//			// normal function body here
//		}
//
//		It is very important that this macro appear in each
//		function, prior to any calls into MFC.  This means that
//		it must appear as the first statement within the 
//		function, even before any object variable declarations
//		as their constructors may generate calls into the MFC
//		DLL.
//
//		Please see MFC Technical Notes 33 and 58 for additional
//		details.
//

/////////////////////////////////////////////////////////////////////////////
// CLegacyApp

#if 0
BEGIN_MESSAGE_MAP(CLegacyApp, CWinApp)
	//{{AFX_MSG_MAP(CLegacyApp)
		// NOTE - the ClassWizard will add and remove mapping macros here.
		//    DO NOT EDIT what you see in these blocks of generated code!
	//}}AFX_MSG_MAP
END_MESSAGE_MAP()

/////////////////////////////////////////////////////////////////////////////
// CLegacyApp construction

CLegacyApp::CLegacyApp()
{
	// TODO: add construction code here,
	// Place all significant initialization in InitInstance
}

/////////////////////////////////////////////////////////////////////////////
// The one and only CLegacyApp object

CLegacyApp theApp;
#endif

char* EXPORT MyAppend(char* in, char* arg1, char *arg2, char*arg3,BOOL last)
{
  CString dest;
  int len=0;
  dest.Format("%s,%s,%s",arg1,arg2,arg3);
  len = dest.GetLength() + sizeof(int)+2; // for size (as int), ; and \0
  if (in==NULL) {
    in = (char*)malloc(len);
    *((int*)in) = len;
    in+=sizeof(int);
    *in = 0;
  } else {
    int wantedsize = (strlen(in)+len);
    in-=sizeof(int);
    if (*((int*)in)<wantedsize) {
      in = (char*)realloc(in,wantedsize);
      *((int*)(in))=wantedsize;
    }
    in+=sizeof(int);
  }
  strcat(in,dest);
  if (!last) strcat(in,";");
  return in;
}

void EXPORT KillBuffer(char* in)
{
  if (in!=NULL) free(in-sizeof(int));
}