This example uses WinDdePostMsg to request a security item from the server once it has received an acknowledgement (via WM_DDEINITIATEACK) to the WinDdeInitiate call. Note the use of the shared memory segment to pass and receive necessary information.

#define INCL_WINDDE             /* Window DDE Functions         */
#define INCL_DOSMEMMGR          /* Memory Manager values        */
#include <os2.h>

BOOL  fSuccess;         /* success indicator                    */
HWND  hwndClient;       /* client window                        */
HWND  hwndServer;       /* server window                        */
CHAR  pszAppName[15]="";/* server application                   */
CHAR  pszTopicName[15]="";/* topic                              */
HWND  hwndTo;           /* target window                        */
HWND  hwndFrom;         /* source window                        */
USHORT  usMsgId;        /* message id                           */
BOOL  fRetry;           /* retry indicator                      */
CONVCONTEXT Context;
PDDESTRUCT  pddeData;   /* DDE structure                        */
MRESULT  mresReply;     /* message return data                  */

case WM_CREATE:
     fSuccess = WinDdeInitiate(hwndClient, pszAppName,
                               pszTopicName, &Context);
     DosAllocSharedMem((PVOID)pddeData,"DDESHAREMEM",
                       sizeof(DDESTRUCT) + 50,
                       PAG_READ | PAG_WRITE | PAG_COMMIT |
                       OBJ_GIVEABLE | OBJ_GETTABLE);

case WM_DDE_INITIATEACK:
     /* issue a request message to DDE partner */
     usMsgId = WM_DDE_REQUEST;

     /* initialize DDE conversation structure */
     pddeData->cbData = sizeof(DDESTRUCT);      /* Total length  */
     pddeData->fsStatus = DDE_FACK;    /* Status - positive ack  */
     pddeData->usFormat = DDEFMT_TEXT;           /* Data format  */
     pddeData->offszItemName = sizeof(DDESTRUCT);/* Offset to item  */

     /* set name of item to 'Security', copying the information to
        the shared memory at the end of pddeData */
     strcpy((BYTE *)pddeData + pddeData->offszItem,
            SZDDESYS_ITEM_SECURITY);

     /* Offset to beginning of data (notice additional offset due
        to item information) */

     pddeData->offabData = sizeof(DDESTRUCT) +
                          strlen(SZDDESYS_ITEM_SECURITY);

     /* set name of item to 'Security', copying the information to
        the shared memory at the end of pddeData */
     strcpy((BYTE *)pddeData + pddeData->offszItem,
            SZDDESYS_ITEM_SECURITY);

     fSuccess = WinDdePostMsg(hwndTo, hwndFrom, usMsgId, pddeData,
                              fRetry);