C挂钩/回拨系统

Question

我一直在想如何在C中实现一个钩子系统。任何人都可以给我一些指针或例子吗？

Answer 1

使用函数指针：

struct callbacks { 
    void (*somethingHappened)(void *context); 
    bool (*shouldIDoSomething)(void *context); 
}; 

void doSomethingAwesome(void *operationData, struct callbacks callbacks) 
{ 
    // context is the data you pass to the function 
    if (callbacks.shouldIDoSomething(context)) 
    { 
      // do something 
      callbacks.somethingHappened(context); 
    } 
} 

或者，你可以创建一个调度服务：

struct dictionary 
{ 
    char **keys; 
    void **values;   

    int count; 
}; 

struct list 
{ 
    void **values; 

    int count; 
}; 

// functions to add, remove, etc; 

struct dictionary *callbacks = NULL; 
void registerForDispatch(char *key, void (*callback)(void *)) 
{ 
    if (!callbacks) 
    { 
     callbacks = dictionary_create(10); // dictionary with 10 key/value pairs 
    } 

    if (!dictionary_containsKey(callbacks, key)) 
    { 
     struct list *callBacksForKey = list_create(10); // default 10 callbacks, array should be auto-expanding 

     dictionary_setValue(callbacks, key, arr); 
    } 

    struct list *callBacksForKey = dictionary_getValue(callbacks, key); 

    list_addObject(callBacksForKey, callback); 
} 

void unregisterFromDispatch(char *key, void (*callback)(void *)) 
{ 
    struct list *callBacksForKey = dictionary_getValue(callbacks, key); 

    list_removeObject(callback); 
} 

void sendNotification(char *key, void *context) 
{ 
    struct list *callBacksForKey = dictionary_getValue(callbacks, key); 

    for (int i = 0; list->count; i++) 
    { 
     void (*callback)(void *) = list->values[i]; 
     callback(context); 
    } 
} 

随着第二个解决方案，您有多个听众的优势一个回调。

Answer 2

你可以看到的qsort例如： http://www.cplusplus.com/reference/clibrary/cstdlib/qsort/

/* qsort example */ 
#include <stdio.h> 
#include <stdlib.h> 

int values[] = { 40, 10, 100, 90, 20, 25 }; 

int compare (const void * a, const void * b) 
{ 
    return (*(int*)a - *(int*)b); 
} 

int main() 
{ 
    int n; 
    qsort (values, 6, sizeof(int), compare); 
    for (n=0; n<6; n++) 
    printf ("%d ",values[n]); 
    return 0; 
} 

的qsort需要的函数指针是用于排序的回调。

Answer 3

我不确定你在找什么东西，但是我一直在使用QT/C++开发应用程序，所以我可以给你举个小例子。

首先，声明函数原型，这样

LRESULT CALLBACK LowLevelMouseProc(int nCode, WPARAM wParam, LPARAM lParam); 

然后，你需要设置挂钩，在主要功能，如：

HHOOK mouseHook; 
HINSTANCE appInstance = GetModuleHandle(NULL); 
mouseHook = SetWindowsHookEx(WH_MOUSE_LL, LowLevelMouseProc, appInstance, 0); //set global mouse hook 

，然后你需要定义回调函数，我可以给你我的代码>

//Mouse hook callback function. 

LRESULT CALLBACK LowLevelMouseProc(int nCode, WPARAM wParam, LPARAM lParam){ 


    if (nCode == HC_ACTION) { 

    switch(wParam){ 
    case WM_LBUTTONUP: 
    case WM_RBUTTONUP: 
    case WM_MOUSEWHEEL: 
#ifdef DEBUG 
     w->printText("Scrolling or click"); 
#endif 
     w->save_key("MOUSE"); 
     i++; 
     break; 

    default: break; 
    } 
    } 
    return CallNextHookEx(mouseHook, nCode, wParam, lParam); 

}