How To Write a DDEML Server for Excel and Use it with NetDDE

#include <windows.h>
#include <stdio.h>
#include <ddeml.h>


// Globals...
HSZ g_hszAppName;
HSZ g_hszTopicName;
HSZ g_hszItemName;
int g_count = 0;
DWORD g_idInst = 0;

// Declarations:
HDDEDATA EXPENTRY DdeCallback(UINT type, UINT fmt, HCONV hConv, HSZ hsz1, HSZ hsz2, HDDEDATA hData, DWORD dwData1, DWORD dwData2);

// WinMain()..
int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) {
   
   // Initialize DDEML...
   if(DdeInitialize(&g_idInst, DdeCallback, APPCLASS_STANDARD, 0)) {
      MessageBox(NULL, "DdeInitialize() failed", "Error", MB_SETFOREGROUND);
      return -1;
   }
   
   // Create string handles...
   g_hszAppName = DdeCreateStringHandle(g_idInst, "DdemlSvr", NULL);
   g_hszTopicName = DdeCreateStringHandle(g_idInst, "MyTopic", NULL);
   g_hszItemName = DdeCreateStringHandle(g_idInst, "MyItem", NULL);
   
   if( (g_hszAppName == 0) || (g_hszTopicName == 0) || (g_hszItemName == 0) ) {
      MessageBox(NULL, "DdeCreateStringHandle() failed", "Error", MB_SETFOREGROUND);
      return -2;
   }
   
   // Register DDE server
   if(!DdeNameService(g_idInst, g_hszAppName, NULL, DNS_REGISTER)) {
      MessageBox(NULL, "DdeNameService() failed!", "Error", MB_SETFOREGROUND);
      return -3;
   }
   
   // Create a timer to simulate changing data...
   SetTimer(0,0,1,0);
   
   // Message loop:
   MSG msg;

   while (GetMessage(&msg, NULL, 0, 0))  {
      // On WM_TIMER, change our counter, and update clients...
      if(msg.message == WM_TIMER) {
         g_count++;
         DdePostAdvise(g_idInst, g_hszTopicName, g_hszItemName);
      }
      TranslateMessage(&msg);
      DispatchMessage(&msg);
   }
   
   return msg.wParam;
}


// Our DDE Callback function...
HDDEDATA EXPENTRY DdeCallback(UINT wType, UINT fmt, HCONV hConv, HSZ hsz1, HSZ hsz2, HDDEDATA hData, DWORD dwData1, DWORD dwData2) {

   switch (wType) {
      
   // ----------------------------------------------------------------
   case XTYP_CONNECT:
      // Client is trying to connect. Respond TRUE if we have what they want...
      if ((!DdeCmpStringHandles(hsz1, g_hszTopicName)) &&
         (!DdeCmpStringHandles(hsz2, g_hszAppName)))
         return (HDDEDATA)TRUE;   // SERVER supports Topic|Service
      else
         return FALSE;  // SERVER does not support Topic|Service
      
      // ----------------------------------------------------------------
   case XTYP_ADVSTART:
      // Client starting advisory loop.
      // Say "ok" if we have what they are asking for...   

      if((!DdeCmpStringHandles(hsz1, g_hszTopicName)) &&
         (!DdeCmpStringHandles(hsz2, g_hszItemName)))
         return (HDDEDATA)TRUE;   // SERVER supports Topic|Service
      else
         return FALSE;  // SERVER does not support Topic|Service
      // ----------------------------------------------------------------
            

   case XTYP_ADVREQ:
      
      // Client wants our data. Since this is specific to Excel, we'll
      // go ahead and assume they want XlTable-formatted data. For a
      // generic DDE server, you might want to handle various formats
      // specified by the passed in fmt parameter.

      if(!DdeCmpStringHandles(hsz1, g_hszTopicName) &&
         !DdeCmpStringHandles(hsz2, g_hszItemName)) {

         short xltableData[100];
         
         // tdtTable record...
         xltableData[0] = 0x0010; // tdtTable
         xltableData[1] = 4; // 2 short ints following
         xltableData[2] = 1; // # rows
         xltableData[3] = 1; // # cols
         
         // tdtInt record...
         xltableData[4] = 0x0006;
         xltableData[5] = 2;
         xltableData[6] = (short)g_count;

         return DdeCreateDataHandle(g_idInst, (UCHAR*)xltableData, 2*7, 0, g_hszItemName, fmt, 0);
      }    
      // ----------------------------------------------------------------
   default:
      return (HDDEDATA)NULL;
   }
}