Dynamic Data Exchange (DDE) is a protocol in Windows that allows applications to communicate with each other and share data. One of the functions used in managing DDE is DdeFreeStringHandle. This function is used to free a string handle that was created using the DdeCreateStringHandle function.

Understanding DdeFreeStringHandle

The DdeFreeStringHandle function is part of the Dynamic Data Exchange Management Library in Windows. It is used to release memory allocated for a string handle that is no longer needed. This is crucial for managing resources efficiently and avoiding memory leaks in applications that use DDE for inter-process communication.

Function Syntax

BOOL DdeFreeStringHandle(
  DWORD idInst,
  HSZ   hsz
);

• idInst: The application instance identifier obtained from a previous call to DdeInitialize.
• hsz: The handle to the string that you want to free.

Return Value

The function returns TRUE if successful, or FALSE if it fails.

Practical Example

Below is a simple example demonstrating how to use DdeFreeStringHandle in a Windows application:

#include <windows.h>
#include <ddeml.h>

int main() {
    DWORD idInst = 0;
    HSZ hszString;
    UINT initResult;

    // Initialize the DDEML
    initResult = DdeInitialize(&idInst, NULL, APPCLASS_STANDARD, 0);
    if (initResult != DMLERR_NO_ERROR) {
        printf("DDE Initialization failed.\n");
        return 1;
    }

    // Create a string handle
    hszString = DdeCreateStringHandle(idInst, "ExampleString", CP_WINANSI);
    if (hszString == 0) {
        printf("Failed to create string handle.\n");
        DdeUninitialize(idInst);
        return 1;
    }

    // Use the string handle for your DDE operations here

    // Free the string handle when done
    if (!DdeFreeStringHandle(idInst, hszString)) {
        printf("Failed to free string handle.\n");
    }

    // Uninitialize the DDEML
    DdeUninitialize(idInst);

    return 0;
}

Explanation

1. Initialize DDEML: The DdeInitialize function is called to obtain an instance identifier (idInst). This identifier is used in subsequent DDE operations.

2. Create String Handle: The DdeCreateStringHandle function is used to create a handle for a string. This handle can be used in DDE conversations.

3. Free String Handle: After the string handle is no longer needed, DdeFreeStringHandle is called to release the resources associated with the handle.

4. Uninitialize DDEML: Finally, DdeUninitialize is called to clean up the DDEML resources.

Alternatives

If you are developing new applications, consider using more modern technologies like COM (Component Object Model) or OLE (Object Linking and Embedding) for inter-process communication, as DDE is considered outdated and less secure.