[Windows进程间通信]拷贝数据 WM_COPYDATA

使用WM_COPYDATA进行进程间通信必须依赖Windows的消息机制，不过此方法可以传输大量数据，而且实现简单。

以下示例修改自Windows官方文档。

首先创建2个Windows桌面程序，为了示例的简单，将字符类型修改为多字节（默认为unicode）。

发送端：

#define MYDISPLAY 1
typedef struct tagMyRec {
    char s1[64];
    char s2[64];
    DWORD n;
} MYREC;

VOID CopyData(HWND hWnd) {

    COPYDATASTRUCT myCDS = {0};
    MYREC myRec = {0};

    // Put data into data structure
    auto hResult = StringCbCopy(myRec.s1, sizeof(myRec.s1), "Claude");
    if (hResult != S_OK) {
        return ;
    }

    hResult = StringCbCopy(myRec.s2, sizeof(myRec.s2), "Bell");
    if (hResult != S_OK) {
        return ;
    }

    myRec.n = 99;

    // Fill COPYDATA structure
    myCDS.dwData = MYDISPLAY;
    myCDS.cbData = sizeof(myRec);
    myCDS.lpData = &myRec;

    auto hwDispatch = FindWindow("RECEIVER", "r");
    if (hwDispatch != NULL) {
        SendMessage(hwDispatch, 
            WM_COPYDATA, 
            (WPARAM)hWnd, 
            (LPARAM)(LPVOID)&myCDS);
    }
    else {
        MessageBox(hWnd, "Can't send WM_COPYDATA", "MyApp", MB_OK);
    }
}

////////////////////////

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
    case WM_COMMAND:
        {
            int wmId = LOWORD(wParam);
            // Parse the menu selections:
            switch (wmId)
            {
            case IDM_ABOUT:
                //DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);
                CopyData(hWnd);

出于示例的简化目的，直接使用IDM_ABOUT触发拷贝数据消息.

接收端：

#define MYDISPLAY 1
typedef struct tagMyRec {
    char s1[64];
    char s2[64];
    DWORD n;
} MYREC;

VOID HandleCopyData(HWND hWnd, WPARAM wparam, LPARAM lparam) {
    auto pCDS = (PCOPYDATASTRUCT)lparam;
    switch (pCDS->dwData) {
    case MYDISPLAY: {
        auto myRec = (MYREC*)pCDS->lpData;
        MessageBox(hWnd, myRec->s1, myRec->s2, MB_OK);
        break;
    }
    }
}

///////////////////////////////

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
    case WM_COPYDATA:
        HandleCopyData(hWnd, wParam, lParam);
        break;

接收端只要在消息处理函数中直接收一下数据就行了。