lib for realtimeMM funcs
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callbacknotes.cpp
00001 /* 00002 00003 Because a member function is meaningless without an object to invoke it on, you can’t do this directly (if The X Window System was rewritten in C++, it would probably pass references to objects around, not just pointers to functions; naturally the objects would embody the required function and probably a whole lot more). 00004 00005 As a patch for existing software, use a top-level (non-member) function as a wrapper which takes an object obtained through some other technique. Depending on the routine you’re calling, this “other technique” might be trivial or might require a little work on your part. The system call that starts a thread, for example, might require you to pass a function pointer along with a void*, so you can pass the object pointer in the void*. Many real-time operating systems do something similar for the function that starts a new task. Worst case you could store the object pointer in a global variable; this might be required for Unix signal handlers (but globals are, in general, undesired). In any case, the top-level function would call the desired member function on the object. 00006 00007 Here’s an example of the worst case (using a global). Suppose you want to call Fred::memberFn() on interrupt: 00008 00009 class Fred { 00010 public: 00011 void memberFn(); 00012 static void staticMemberFn(); // A static member function can usually handle it 00013 // ... 00014 }; 00015 // Wrapper function uses a global to remember the object: 00016 Fred* object_which_will_handle_signal; 00017 void Fred_memberFn_wrapper() 00018 { 00019 object_which_will_handle_signal->memberFn(); 00020 } 00021 int main() 00022 { 00023 signal(SIGINT, Fred::memberFn); // Can NOT do this 00024 signal(SIGINT, Fred_memberFn_wrapper); // Okay 00025 signal(SIGINT, Fred::staticMemberFn); // Okay usually; see below 00026 } 00027 Note: static member functions do not require an actual object to be invoked, so pointers-to-static-member-functions are usually type-compatible with regular pointers-to-functions. However, although it probably works on most compilers, it actually would have to be an extern "C" non-member function to be correct, since “C linkage” doesn’t only cover things like name mangling, but also calling conventions, which might be different between C and C++. 00028 00029 Test 00030 */
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