如何從事件函式中回傳一個變數？

我是 C/C 新手。目前，我正在做一個使用觸覺設備的專案。我只想在按下設備按鈕時回傳一個值，下面是我的代碼。

#ifdef  _WIN64
#pragma warning (disable:4996)
#endif

#include <stdio.h>
#include <assert.h>

#if defined(WIN32)
# include <conio.h>
#else
# include "conio.h"
#endif

#include <HD/hd.h>
#include <HL/hl.h>

#include <HDU/hduError.h>

int HLCALLBACK buttonCB(HLenum event, HLuint object, HLenum thread, 
                       HLcache *cache, void *userdata);

/*******************************************************************************
 Main function.
*******************************************************************************/
int btn;
int main(int argc, char *argv[])
{
    HHD hHD;
    HHLRC hHLRC;
    HDErrorInfo error;
    HLerror frameError;

    hHD = hdInitDevice(HD_DEFAULT_DEVICE);
    if (HD_DEVICE_ERROR(error = hdGetError())) 
    {
        hduPrintError(stderr, &error, "Failed to initialize haptic device");
        fprintf(stderr, "\nPress any key to quit.\n");
        getch();
        return -1;
    }
    hdMakeCurrentDevice(hHD);    
    hHLRC = hlCreateContext(hHD);
    hlMakeCurrent(hHLRC);

    /* Add a callback to handle button down in the collision thread. */
    hlAddEventCallback(HL_EVENT_1BUTTONDOWN, HL_OBJECT_ANY, HL_CLIENT_THREAD, 
                       buttonCB, 0);
    hlAddEventCallback(HL_EVENT_2BUTTONDOWN, HL_OBJECT_ANY, HL_CLIENT_THREAD, 
                       buttonCB, 0);

    printf("Move around to feel the ambient stick-slip friction.\n\n");
    printf("Press and hold the primary stylus button to feel the spring effect.\n\n");
    printf("Press the second stylus button to trigger an impulse.\n\n");

    /* Run the main loop. */
    while (!_kbhit())
    {
        hlCheckEvents();
        Sleep(3000);

    }
    hlDeleteContext(hHLRC);
    hdDisableDevice(hHD);

    return 0;
}

void HLCALLBACK buttonCB(HLenum event, HLuint object, HLenum thread, 
                         HLcache *cache, void *userdata)
{
    int btn;
    if (event == HL_EVENT_1BUTTONDOWN)
    {
        btn = 1;
        printf("Button 1 pressed %d ", btn);
        return btn;
    }
    else if (event == HL_EVENT_2BUTTONDOWN)
    {
        btn = 2;
        printf("Button 2 pressed %d ", btn);
        return btn;

    }
}

/******************************************************************************/

buttonCB 回呼函式用作事件。使用此命令在主回圈中檢查這些按鈕事件hlCheckEvents();。在代碼中，您可以看到HLCALLBACK buttonCB按下按鈕時觸發事件的 int 函式。我希望當按下按鈕時，事件應該將一個值存盤在一個btn可以從主函式訪問的變數中。請幫我解決這個問題。

uj5u.com熱心網友回復：

您可以userData用來傳輸資料，例如：

int button = 0; // Should be valid as long as event might be called.

/* Add a callback to handle button down in the collision thread. */
hlAddEventCallback(HL_EVENT_1BUTTONDOWN, HL_OBJECT_ANY, HL_CLIENT_THREAD, 
                   buttonCB, &button);
hlAddEventCallback(HL_EVENT_2BUTTONDOWN, HL_OBJECT_ANY, HL_CLIENT_THREAD, 
                   buttonCB, &button);
// ..

/* Run the main loop. */
while (!_kbhit())
{
    // button = 0; // Potentially reinit here
    hlCheckEvents();
    printf("button value: %d", button); // Do work with last value
    Sleep(3000);
}

然后你的回呼

void HLCALLBACK buttonCB(HLenum event, HLuint object, HLenum thread, 
                         HLcache *cache, void *userdata)
{
    int* button = (int*) userdata;
    if (event == HL_EVENT_1BUTTONDOWN)
    {
        *button = 1;
        printf("Button 1 pressed %d ", btn);
    }
    else if (event == HL_EVENT_2BUTTONDOWN)
    {
        *button = 1; = 2;
        printf("Button 2 pressed %d ", btn);
    }
}

uj5u.com熱心網友回復：

我不是很喜歡事件處理。但我會盡力提供幫助。

您正在從函式回傳 btn，該函式的型別為 int，但函式回傳型別為 void，這意味著該函式不能回傳任何內容。所以，修復很簡單。將 buttonCB 函式的回傳型別從 void 更改為 int：

/*void*/ int HLCALLBACK buttonCB(HLenum event, HLuint object, HLenum thread, 
                         HLcache *cache, void *userdata)
{
    int btn;
    if (event == HL_EVENT_1BUTTONDOWN)
    {
        btn = 1;
        printf("Button 1 pressed %d ", btn);
        return btn;
    }
    else if (event == HL_EVENT_2BUTTONDOWN)
    {
        btn = 2;
        printf("Button 2 pressed %d ", btn);
        return btn;

    }
}

現在函式的回傳型別是 int，這是您要回傳的 btn 變數的型別。

標籤：C 多线程 温纳皮 事件处理

上一篇：C 無法使用PROCESSENTRY32編譯代碼

下一篇：從RVA中查找檔案的函式偏移量