The C ++ class member method is directly used as a thread callback function.

When I used to write a thread, I either honestly follow the declaration or use the static member function of the C ++ class as the callback function. The encapsulation is often broken due to the thread code. although I knew the expansion form of class member functions before, I never thought about using it. I learned this trick when I went deep into ATL yesterday. :) the class member method is a special function, it will be converted into a common function during compilation. For example, the TMyClass class: class TMyClass {void Func () ;}; TMyClass :: func will eventually be converted to void Func (TMyClass * this); that is to say, insert the this pointer to the object itself before the original first parameter. We can use this feature to write a non-static class member method to directly act as a thread callback function. first look at the definition of the _ beginthread function: unsigned long _ RTLENTRY _ EXPFUNC _ beginthread (void (_ USERENTRY * _ start) (void *), unsigned _ stksize, void * _ arg ); the first parameter is the callback function used as the thread execution subject. Its prototype is void Func (void *). This void * parameter is passed in as custom data. Compare the final form of TMyClass: Func mentioned above, which can meet the requirements here. Now let's do an experiment: # include <stdio. h> # include <process. h> class TMyClass {int m_nCount; int m_nId; public: TMyClass (int nId, int nCount): m_nId (nId), m_nCount (nCount) {} void _ userthreadentry proc () // Class member method {for (int I = 0; I <m_nCount; I ++) // print a row of numbers based on m_nCount members {printf ("Class % d: % d \ n ", m_nId, I) ;}}; int main (int argc, char * argv []) {// Union class, it is used to convert the method pointer of a class member to a normal function pointer (the compiler does not allow forced conversion between the two functions). I wonder if there is any better method. Union {void (_ USERENTRY * ThreadProc) (void *); void (_ USERENTRY TMyClass: * MemberProc) ();} Proc; // although the two function types in the Union seem very different now, their final forms are the same. TMyClass MyClass1 (), MyClass2 (); // generate two TMyClass objects: Proc. memberProc = & TMyClass: ThreadProc; // conversion, Proc. threadProc is the corresponding normal function pointer _ beginthread (Proc. threadProc, 4096, & MyClass1); // start thread, Here Proc. threadProc is actually TMyClass: ThreadProc, And the this pointer it requires is what we give & MyClass1. _ Beginthread (Proc. ThreadProc, 4096, & MyClass2); system ("pause"); return 0 ;} run! Magic? :-) In fact, not only the thread callback function, but as long as the callback function is like Func (void *,...), you can use this method to directly use the class member method. (The premise is that the first void * is custom data, that is, it cannot have other functions ).