ChemDraw DDE
Transaction Types

1. Execute Transactions [The server receives the command string in the "hData" item.] Example of usage from the client side, using DDEML:
   
   const char data[] = "OPEN D:\mf\strychnine.chm";
   HDDEDATA retval;
   
   retVal = DdeClientTransaction (
   data,           // the command
   strlen(data)+1, //len of data, incl. term. null
   m_hConv,        //handle of the conversation
   0,              //handle of item name string
   0,               //clipboard data format
   XTYP_EXECUTE,   //transaction type
   5000,           //timeout: 5 seconds
   &result);       //transaction result
   
   BOOL success = (retVal != NULL);
2. Request transactions [The server receives the command string in the "item name."] The returned data has the format:

   	status	msg len	msg	command-specific data
   bytes:	1	1	0+	0+

   The message, if present, is not null-terminated.
   
   Example of usage from the client side:
   
   const char data[] = "MAKE_METAFILE
                        D:\mf\strychnine.chm";
   HDDEDATA retval;
   
   retVal = DdeClientTransaction (
   NULL,           //no arg expected
   0,              //len of the preceding arg
   m_hConv,        //handle of the conversation
   MakeStringHandle (data)  //handle of a data item
   CF_TEXT,        //clipboard data format
   XTYP_REQUEST,   //transaction type
   15000,          //timeout: 15 seconds
   &result);       //transaction result
   
   if (retVal) {
     numBytes = DdeGetData (retVal, NULL, 0, 0);
     BYTE buf = malloc (numBytes);
     DWORD numBytesCopied = DdeGetData (retVal, buf,
                            numBytes, 0); //0=offset
   
     BYTE b2 [2];
   
     DdeGetData (retVal, b2, 2, 0); //get first two                                  //bytes
   
     BOOL success = b2 [0];
   
     //There will be an error string, i.e. b2[1]
     //non-zero, if and only if success is False.
   
     if (!success) {
       char *errMsg = new char [b2 [1]];
   
       // 2=offset
       DdeGetData (retVal, errMsg, b2 [1], 2);
       MessageBox (errMsg);
     }
     else {
       // If the command returns special data, it
       //resides at offset (2 + b2[1]).
     }
   }

3. Advise Loop ("warm") Transactions There is only one usage of an advise loop in the server, viz. in conjunction with the EDIT command, to notify the client whenever its structure being edited in ChemDraw changes. The value of the datum passed from client to server in the advise loop request is "Changed " plus the full path name of the temporary disk file through which edit changes are communicated. The advise loop should be set up after the EDIT command has been issued. The filename referenced in the Advise Loop command should be identical to that issued in the EDIT command. The client initially writes this file, ChemDraw picks it up, updates it periodically, notifying the client when it does so. Example of setting up the advise loop from the client side, using DDEML:
   
   //note space after "Changed"
   const char data[] = "CHANGED " + filename;
   HDDEDATA retval;
   
   retVal = DdeClientTransaction (
   NULL,           //no arg expected
   0,              //length of the preceding arg
   m_hConv,        //handle of the conversation
   MakeStringHandle (data)  //handle of a data item
   CF_TEXT,        //clipboard data format
   XTYP_ADVSTART,  //transaction type
   5000,           //timeout: 5 seconds
   &result);       //transaction result
   
   BOOL success = (retVal != NULL);
   
   where MakeStringHandle amounts to:
   
   return DdeCreateStringHandle (gDDE_instance, data,                                 CP_WINANSI);