The DdeClientTransaction function begins a data transaction between a client and a server. Only a dynamic data exchange (DDE) client application can call this function, and the application can use it only after establishing a conversation with the server.
HDDEDATA DdeClientTransaction(
LPBYTE pData, |
// pointer to data to pass to server |
DWORD cbData, |
// length of data |
HCONV hConv, |
// handle to conversation |
HSZ hszItem, |
// handle to item name string |
UINT wFmt, |
// clipboard data format |
UINT wType, |
// transaction type |
DWORD dwTimeout, |
// time-out duration |
LPDWORD pdwResult |
// pointer to transaction result |
); |
Optionally, an application can specify the data handle (HDDEDATA) to pass to the server and in that case the cbData parameter should be set to 0xFFFFFFFF. This parameter is required only if the wType parameter is XTYP_EXECUTE or XTYP_POKE. Otherwise, this parameter should be NULL.
For the optional usage of this parameter, XTYP_POKE transactions where pData
is a data handle, the handle must have been created by a previous call to the DdeCreateDataHandle
function, employing the same data format specified in the wFmt
parameter.
If the transaction specified by the wType parameter does not pass data or is XTYP_EXECUTE, this parameter should be zero.
If the transaction specified by the wType parameter references
non-execute DDE data (XTYP_POKE, XTYP_ADVSTART, XTYP_ADVSTOP, XTYP_REQUEST),
the wFmt value must be either a valid predefined (CF_) DDE format or a
valid registered clipboard format.
Type |
Meaning |
Begins an advise loop. Any number of distinct advise loops can exist within a conversation. An application can alter the advise loop type by combining the XTYP_ADVSTART transaction type with one or more of the following flags: |
Flag |
Meaning |
XTYPF_NODATA |
Instructs the server to notify the client of any data changes without actually sending the data. This flag gives the client the option of ignoring the notification or requesting the changed data from the server. |
XTYPF_ACKREQ |
Instructs the server to wait until the client acknowledges that it received the previous data item before sending the next data item. This flag prevents a fast server from sending data faster than the client can process it. |
Ends an advise loop. | |
Begins an execute transaction. | |
Begins a poke transaction. | |
Begins a request transaction. |
If the function succeeds, the return value is a data handle that identifies the data for successful synchronous transactions in which the client expects data from the server. The return value is nonzero for successful asynchronous transactions and for synchronous transactions in which the client does not expect data. The return value is zero for all unsuccessful transactions.
The DdeGetLastError function can be used to get the error code, which may be one of the following values:
DMLERR_ADVACKTIMEOUT
DMLERR_BUSY
DMLERR_DATAACKTIMEOUT
DMLERR_DLL_NOT_INITIALIZED
DMLERR_EXECACKTIMEOUT
DMLERR_INVALIDPARAMETER
DMLERR_MEMORY_ERROR
DMLERR_NO_CONV_ESTABLISHED
DMLERR_NO_ERROR
DMLERR_NOTPROCESSED
DMLERR_POKEACKTIMEOUT
DMLERR_POSTMSG_FAILED
DMLERR_REENTRANCY
DMLERR_SERVER_DIED
DMLERR_UNADVACKTIMEOUT
When an application has finished using the data handle returned by DdeClientTransaction, the application should free the handle by calling the DdeFreeDataHandle function.
Transactions can be synchronous or asynchronous. During a synchronous transaction, DdeClientTransaction does not return until the transaction either completes successfully or fails. Synchronous transactions cause a client to enter a modal loop while waiting for various asynchronous events. Because of this, a client application can still respond to user input while waiting on a synchronous transaction, but the application cannot begin a second synchronous transaction because of the activity associated with the first. DdeClientTransaction fails if any instance of the same task has a synchronous transaction already in progress.
During an asynchronous transaction, DdeClientTransaction returns after the transaction has begun, passing a transaction identifier for reference. When the server’s DDE callback function finishes processing an asynchronous transaction, the system sends an XTYP_XACT_COMPLETE transaction to the client. This transaction provides the client with the results of the asynchronous transaction that it initiated by calling DdeClientTransaction. A client application can choose to abandon an asynchronous transaction by calling the DdeAbandonTransaction function.
DdeAbandonTransaction, DdeAccessData, DdeConnect, DdeConnectList, DdeCreateDataHandle, DdeCreateStringHandle, DdeFreeDataHandle, XTYP_ADVSTART, XTYP_ADVSTOP, XTYP_EXECUTE, XTYP_POKE, XTYP_REQUEST
file: /Techref/os/win/api/win32/func/src/f13_5.htm, 11KB, , updated: 2000/4/7 12:19, local time: 2024/8/23 11:46,
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