物件中函數參數是另一個函數指標的問題？ |
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尚未結案
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hornacek
一般會員   發表：29 回覆：76 積分：21 註冊：2004-02-02 發送簡訊給我 |
程式碼如下：
class A
{
private:
void func(void);
void func2(void (*func)(void));
void func3(void);
}; void A::func(void)
{
}
void A::func2(void (*func)(void))
{
}
void A::func3(void)
{
func2(func);
}
編譯之後出現
Cannot convert 'void (*(__closure )())()' to 'void (*)()'
Type mismatch in parameter 'func' (wanted 'void (*)()', got 'void')
的錯誤？請問我是哪裡用錯了？謝謝！ 把func3改成
void A::func3(void)
{
func2(::func);
}
編譯後出現
Undefined symbol 'func'
的錯誤訊息？請問這到底是怎麼回事？
我要如何使用函數指標當作函數的參數呢？謝謝！
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pwipwi
版主  發表：68 回覆：629 積分：349 註冊：2004-04-08 發送簡訊給我 |
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hornacek
一般會員 發表：29 回覆：76 積分：21 註冊：2004-02-02 發送簡訊給我 |
引言: hornacek你好： 參考一下http://delphi.ktop.com.tw/topic.php?TOPIC_ID=56371 不知道能否解決你的問題？謝謝！我的問題解決了！不過不是很清楚為什麼？ 只要加上__closure關鍵字，如下：
class A
{
private:
void func(void);
void func2(void (__closure *func)(void));
void func3(void);
}; void A::func(void)
{
}
void A::func2(void (__closure *func)(void))
{
}
void A::func3(void)
{
func2(func);
}
以下是BCB Help對於__closure的說明 __closure The __closure keyword is used to declare a special type of pointer to a member function. Unlike a regular C member function pointer, a closure contains an object pointer.
In standard C , you can assign a derived class instance to a base class pointer; however, you cannot assign a derived class? member function to a base class member function pointer. The following code illustrates this:
class base {
public:
void func(int x);
}; class derived: public base {
public:
void new_func(int i);
}; void (base::*bptr)(int); bptr = &derived::new_func; // illegal
However, the __closure language extension allows you to do this in C Builder. A closure associates a pointer to a member function with a pointer to a class instance. The pointer to the class instance is used as the this pointer when calling the associated member function. A closure declaration is the same as a function pointer declaration but with the addition of the __closure keyword before the identifier being defined. For example:
struct MyObject {
double MemFunc(int);
}; double func1(MyObject *obj) {
// A closure taking an int argument and returning double.
double ( __closure *myClosure )(int); // Initialize the closure. myClosure = obj -> MemFunc; // Use the closure to call the member function and pass it an int. return myClosure(1);
}
Although the preceding discussion illustrates closures by assigning descendant class methods, you can assign any class method pointer to a closure. That is, closures allow completely disparate classes to share a method pointer.
Closures are used with events in C Builder.
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發表時間：2004-09-30 00:52:38
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系統時間：2024-06-02 13:46:08
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