function-pointers

问题 I found something interesting. The error message says it all. What is the reason behind not allowing parentheses while taking the address of a non-static member function? I compiled it on gcc 4.3.4. #include <iostream> class myfoo{ public: int foo(int number){ return (number*10); } }; int main (int argc, char * const argv[]) { int (myfoo::*fPtr)(int) = NULL; fPtr = &(myfoo::foo); // main.cpp:14 return 0; } Error: main.cpp:14: error: ISO C++ forbids taking the address of an unqualified or

问题 I understand I can use pointers for functions. Can someone explain why one would use them, and how? Short example code would be very helpful to me. 回答1: A simple case is like this: You have an array of operations (functions) according to your business logic. You have a hashing function that reduces an input problem to one of the business logic functions. A clean code would have an array of function pointers, and your program will deduce an index to that array from the input and call it. Here

问题 I can create function pointers in Fortran 90, with code like real, external :: f and then use f as an argument to another function/subroutine. But what if I want an array of function pointers? In C I would just do double (*f[])(int); to create an array of functions returning double and taking an integer argument. I tried the most obvious, real, external, dimension(3) :: f but gfortran doesn\'t let me mix EXTERNAL and DIMENSION. Is there any way to do what I want? (The context for this is a

问题 I have a third-party library which has a method that takes a function pointer as the first parameter: int third_party_method(void (*func)(double*, double*, int, int, double*), ...); I want to pass a pointer to a class\' method that is declared as follows: class TestClass { public: void myFunction (double*, double*, int, int, void*); I tried to pass this function as follows: TestClass* tc = new TestClass(); using namespace std::placeholders; third_party_method(std::bind(&TestClass::myFunction,

问题 I have a list of pointers to member functions but I am having a difficult time trying to call those functions... whats the proper syntax? typedef void (Box::*HitTest) (int x, int y, int w, int h); for (std::list<HitTest>::const_iterator i = hitTestList.begin(); i != hitTestList.end(); ++i) { HitTest h = *i; (*h)(xPos, yPos, width, height); } Also im trying to add member functions to it here std::list<HitTest> list; for (std::list<Box*>::const_iterator i = boxList.begin(); i != boxList.end();

问题 I\'m trying to call a function that takes an argument, void(*)(void*, int, const char*) , but I cannot figure out how to pass those arguments to the function. Example: void ptr(int); int function(int, int, void(*)(int)); I am trying to call the function like this: function(20, 20, ptr(20)); Is this possible? 回答1: You are doing one thing incorrectly - you are trying to invoke your 'ptr' function before invoking 'function'. What you were supposed to do is to pass just a pointer to 'ptr' and

问题 I have a void pointer returned by dlsym(), I want to call the function pointed by the void pointer. So I do a type conversion by casting: void *gptr = dlsym(some symbol..) ; typedef void (*fptr)(); fptr my_fptr = static_cast<fptr>(gptr) ; I have also tried reinterpret_cast but no luck, although the C cast operator seems to work.. 回答1: Converting a void* to a function pointer directly is not allowed (should not compile using any of the casts) in C++98/03. It is conditionally supported in C++0x

问题 1) Misconception : Whenever an array is declared in C language, a pointer to the first element of the array is created (the name of the array) implicitly. (Is it? I don\'t think so!) The first two lines of this page (though I am not sure about the correctness of the information) state the same. As we have seen, when we declare an array, a contiguous block of memory is allocated for the cells of the array and a pointer cell (of the appropriate type) is also allocated and initialized to point

问题 How can i hash (std::tr1::hash or boost::hash) a c++ pointer-to-member-function? Example: I have several bool (Class::*functionPointer)() (not static) that point to several diferent methods of the class Class and i need to hash those pointer-to-member-function. How can i do that? Also how can i compare (std::less) those member function pointers so i can store them in a std::set? 回答1: All C++ objects, including pointers to member functions, are represented in memory as an array of chars. So

问题 I developed a scripting engine that has many built-in functions, so to call any function, my code just went into an if .. else if .. else if wall checking the name but I would like to develop a more efficient solution. Should I use a hashmap with strings as keys and pointers as values? How could I do it by using an STL map? EDIT : Another point that came into my mind: of course using a map will force the compiler not to inline functions, but my inefficient approach didn\'t have any overhead