c++ - 如何在 DdeCallback 函数中实现返回码

Question

编写DdeCallback 函数的正确方法是什么？更准确地说，我说的是返回码。

来自官方docs :

The return value depends on the transaction class. For more information about the return values, see descriptions of the individual transaction types

例如，我的应用程序需要自己处理XTYP_ADVDATA 消息并忽略其他消息。

所以，根据docs对于 XTYP_ADVDATA，如果我处理了这条消息，我需要返回 DDE_FACK:

A DDE callback function should return DDE_FACK if it processes this transaction, DDE_FBUSY if it is too busy to process this transaction, or DDE_FNOTPROCESSED if it rejects this transaction

但是其他消息呢？其他情况应该返回什么？

//初始化

DWORD id_inst = 0;
UINT res = DdeInitializeA(
  &id_inst,
  (PFNCALLBACK)DdeCallback,
  APPCLASS_STANDARD | APPCMD_CLIENTONLY,
  0 // Reserved; must be set to zero
);

// XTYP_ADVSTART

HDDEDATA data = DdeClientTransaction(
  NULL,   // The beginning of the data the client must pass to the server. This parameter is required only if the wType parameter is XTYP_EXECUTE or XTYP_POKE. Otherwise, this parameter should be NULL
  0,      // The length, in bytes, of the data pointed to by the pData parameter
  conv,
  item,
  CF_TEXT,
  XTYP_ADVSTART,
  30000,  // The maximum amount of time, in milliseconds, that the client will wait for a response from the server application in a synchronous transaction
  NULL    // A pointer to a variable that receives the result of the transaction. An application that does not check the result can use NULL for this value
);

HDDEDATA CALLBACK DdeCallback(
  UINT uType,     // The transaction type
  UINT uFmt,      // The format atom of the data sent from the server
  HCONV hconv,    // A handle to the conversation
  HSZ hsz1,       // A handle to the topic name
  HSZ hsz2,       // A handle to the item name
  HDDEDATA hdata, // A handle to the data associated with the topic name and item name pair
  DWORD dwData1,  // Not used
  DWORD dwData2)  // Not used
{
  switch (uType)
  {
  case XTYP_ADVDATA:
    DWORD data_size = DdeGetData(hdata, NULL, 0, 0);
    std::unique_ptr<char[]> buf(new char[data_size]);
    DdeGetData(
      hdata,
      (BYTE *)buf.get(),
      data_size,
      0 // An offset within the DDE object. Data is copied from the object beginning at this offset
    );
    std::cout << "Data received: " << buf.get() << std::endl;
    return (HDDEDATA)DDE_FACK;
  }

  return /* ??? */;
}

Answer 1

调用 DdeInitialize() 时，您只会收到您注册的消息类型(或者更准确地说，您没有过滤掉的消息类型)。如果您只注册接收(或不忽略)XTYP_ADVDATA 消息，那么您将收到这些消息，您不必担心处理其他消息类型。根据每种消息类型的规则，您必须在回调中正确处理您未过滤掉的任何消息类型。

阅读 DdeInitialize() 的文档，注意其 afCmd 参数的说明。另请阅读有关 DDE 的文档 Basic Concepts ，特别是描述 Initialization 的部分和 Callback function .