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POOn writing win32 api wrapper with C++, how to pass this pointer to static function
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copied!<p>I want to convert function object to function.</p> <p>I wrote this code, but it doesn't work.</p> <pre><code>#include <iostream> typedef int (*int_to_int)(int); struct adder { int n_; adder (int n) : n_(n) {} int operator() (int x) { return x + n_; } operator int_to_int () { return this->*&adder::operator(); } }; int main(void) { adder add_two(2); int_to_int add_fn = add_two; std::cout << add_two(3) << std::endl; // expect 5 std::cout << add_fn(3) << std::endl; // expect 5 add_fn = adder(5); std::cout << add_fn(3) << std::endl; // expect 8 return 0; } </code></pre> <p>and I got message from g++, says <code>invalid use of non-static member function</code>.</p> <p>How do I get pointer to member function of instance?</p> <p><strong>Edit</strong>:My original problem is about Win32 API.</p> <p>I'm forced to write windows program with old Win32 API at school. but I don't want to write horrible switch statement like some example codes on text. Then, I decided to write wrapper in C++.</p> <p>I want to write the window class like ... </p> <pre><code>class Window { public: LRESULT update (HWND, UINT, WPARAM, LPARAM); void run(); // below methods are called by update() virtual void onclick(int, int); virtual void ondraw(); // ... and more methods }; </code></pre> <p>and I'm willing to write my application class with deriving this class and overloading some methods.</p> <p>Finally, my actual probrem is how to do this in C++.</p> <pre><code> // on initializing my window object, // I must register window class with callback which is // not a C++ function object. // I try to explain what I want to do with psudocode mixing C++ and javascript. WNDCLASS wndclass; Window *self = this; wndclass.lpfnWndProc = function () { return self.update.apply(self, argunemts); }; </code></pre> <p>In other word, I have to make closure into function pointer. I don't know how to do this, but I can't believe this can't do in C++.</p> <p><strong>Edit</strong>: The original title of this question was <em>How to get pointer-to-member-function of instance</em>. But this title and my question didn't tell my actual problem enough. Sorry to early answerers, and litb, thank you for suggestion and very useful answer!</p>

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