我希望有人能解释一下这个让我困惑的代码片段。
//-------------------------------------------------------------------------------
// 3.5 Example B: Callback to member function using a global variable
// Task: The function 'DoItB' does something that implies a callback to
// the member function 'Display'. Therefore the wrapper-function
// 'Wrapper_To_Call_Display is used.
#include <iostream.h> // due to: cout
void* pt2Object; // global variable which points to an arbitrary object
class TClassB
{
public:
void Display(const char* text) { cout << text << endl; };
static void Wrapper_To_Call_Display(char* text);
/* more of TClassB */
};
// static wrapper-function to be able to callback the member function Display()
void TClassB::Wrapper_To_Call_Display(char* string)
{
// explicitly cast global variable <pt2Object> to a pointer to TClassB
// warning: <pt2Object> MUST point to an appropriate object!
TClassB* mySelf = (TClassB*) pt2Object;
// call member
mySelf->Display(string);
}
// function does something that implies a callback
// note: of course this function can also be a member function
void DoItB(void (*pt2Function)(char* text))
{
/* do something */
pt2Function("hi, i'm calling back using a global ;-)"); // make callback
}
// execute example code
void Callback_Using_Global()
{
// 1. instantiate object of TClassB
TClassB objB;
// 2. assign global variable which is used in the static wrapper function
// important: never forget to do this!!
pt2Object = (void*) &objB;
// 3. call 'DoItB' for <objB>
DoItB(TClassB::Wrapper_To_Call_Display);
}
问题 1:关于此函数调用:
DoItB(TClassB::Wrapper_To_Call_Display)
为什么 Wrapper_To_Call_Display
不接受任何参数,尽管根据其声明它应该接受 char*
参数?
问题 2: DoItB
声明为
void DoItB(void (*pt2Function)(char* text))
到目前为止我所理解的是 DoItB
采用函数指针作为参数,但是为什么函数调用 DoItB(TClassB::Wrapper_To_Call_Display)
采用 TClassB::Wrapper_To_Call_Display
作为参数,即使它不是一个指针?
提前致谢
最佳答案
在 C/C++ 中,当使用不带参数的函数名(即没有括号)时,它是指向函数的指针。因此,TClassB::Wrapper_To_Call_Display
是一个指向内存中实现该函数代码的地址的指针。
由于 TClassB::Wrapper_To_Call_Display
是一个指向 void
函数的指针,该函数采用单个 char*
,所以时间是 void ( *)(char* test)
因此它与 DoItB
所需的类型匹配。
关于c++ - 回调非静态 C++ 成员函数,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/10060219/