PRB: Inadequate Buffer Length Causes Strange Problems in DDEML

SYMPTOMS

Specifying an inadequate buffer length for an XTYP_POKE or an XTYP_EXECUTE command causes strange problems in DDEML.

Problems can range from a general protection (GP) fault or Exception 13, to DDEML timeout errors (such as DMLERR_EXECACKTIMEOUT or DMLERR_POKEACKTIMEOUT) or a DDEML transaction failure (or DMLERR_NOTPROCESSED). Sometimes, the application may seem to work for the most part, and then occasionally crash.

Data can be passed to the server application via XTYP_POKE or XTYP_EXECUTE in two ways:

• Directly, as a pointer to the data or command string, as in the sample code below:

     char lpszString [80];
  
     lstrcpy (lpszString, "[FileOpen(""C:\README.DOC"")]");
     DdeClientTransaction (lpszString,             // string buffer
                           lstrlen (lpszString)+1, // string buffer length
                           hConv,
                           hszItem,
                           CF_TEXT,
                           XTYP_POKE,
                           1000,
                           NULL);
  						

-or-

• By creating a data handle, and passing that on to the DdeClientTransaction() call:

     char lpszString [80];
     HDDEDATA hData;
  
     lstrcpy (lpszString, "[FileOpen(""C:\README.DOC"")]");
     hData = DdeCreateDataHandle (idInst,
                                  lpszString,
                                  lstrlen (lpszString)+1,
                                  0,
                                  NULL,
                                  CF_TEXT,
                                  0);
     if (!hData)
        DdeClientTransaction (hData,     // string buffer
                              -1,        // indicates hData is a data handle
                              hConv,
                              hszItem,
                              CF_TEXT,
                              XTYP_POKE,
                              1000,
  						

  NULL);

function does not include the terminating null character, this can