Submitting an Item to the Server - Win32 Programmer's Reference

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Submitting an Item to the Server

The client may send an item value to the server by using the WM_DDE_POKE message. The client renders the item to be sent and sends the WM_DDE_POKE message, as illustrated in the following example.

if (!(hPokeData = GlobalAlloc(GMEM_MOVEABLE | GMEM_DDESHARE,

(LONG) sizeof(DDEPOKE) + lstrlen(szValue) + 2)))

return;

if (!(lpPokeData = (DDEPOKE FAR*) GlobalLock(hPokeData))) {

GlobalFree(hPokeData);

return;

}

lpPokeData->fRelease = TRUE;

lpPokeData->cfFormat = CF_TEXT;

lstrcpy((LPSTR) lpPokeData->Value, (LPSTR) szValue);

/* Each line of CF_TEXT data is terminated by CR/LF. */

lstrcat((LPSTR) lpPokeData->Value, (LPSTR) "\r\n");

GlobalUnlock(hPokeData);

if ((atomItem = GlobalAddAtom((LPSTR) szItem)) != 0) {

if (!PostMessage(hwndServerDDE,

WM_DDE_POKE,

(WPARAM) hwndClientDDE,

PackDDElParam(WM_DDE_POKE, (UINT) hPokeData,

atomItem))) {

GlobalDeleteAtom(atomItem);

GlobalFree(hPokeData);

}

if (atomItem == 0) {

. /* error handling */

}

Note that sending data by using a WM_DDE_POKE message is essentially the same as sending it by using WM_DDE_DATA, except that WM_DDE_POKE is sent from the client to the server.

If the server is able to accept the data-item value in the format rendered by the client, the server processes the item value as appropriate and sends the client a positive WM_DDE_ACK message. If it is unable to process the item value, because of its format or for other reasons, the server sends the client a negative WM_DDE_ACK message.

UnpackDDElParam(WM_DDE_POKE, lParam, (PUINT) &hPokeData,

(PUINT) &atomItem);

GlobalGetAtomName(atomItem, szItemName, ITEM_NAME_MAX_SIZE);

if (!(lpPokeData = (DDEPOKE FAR*) GlobalLock(hPokeData))

|| lpPokeData->cfFormat != CF_TEXT

|| !IsItemSupportedByServer(szItemName)) {

PostMessage(hwndClientDDE,

WM_DDE_ACK,

(WPARAM) hwndServerDDE,

PackDDElParam(WM_DDE_ACK, 0, atomItem)); /* negative ACK */

}

lstrcpy(szItemValue, lpPokeData->Value); /* copies value */

bRelease = lpPokeData->fRelease;

GlobalUnlock(hPokeData);

if (bRelease) {

GlobalFree(hPokeData);

}

PostMessage(hwndClientDDE,

WM_DDE_ACK,

(WPARAM) hwndServerDDE,

PackDDElParam(WM_DDE_ACK,

0x8000, atomItem)); /* positive ACK */

In this example, the server calls GlobalGetAtomName to retrieve the name of the item the client sent. The server then determines whether it supports the item and whether the item is rendered in the correct format (that is, CF_TEXT). If the item is not supported and not rendered in the correct format, or if the server cannot lock the memory for the data, the server sends a negative acknowledgment back to the client application. Note that in this case, sending a negative acknowledgement is correct because WM_DDE_POKE messages are always assumed to have the fAckReq member set. The server should ignore the member.

If a server sends a negative acknowledgement in response to a WM_DDE_POKE message, the client is responsible for freeing the memory (but not the lParam parameter) referenced by the WM_DDE_POKE message associated with the negative acknowledgement.

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