Approach 1 (Virtual Function) “+” The “correct way to do it in C++ “-” A new class must be created per callback “-” Performance-wise an additional dereference through VF-Table compared to Function Pointer. Two indirect references compared to Functor solution. Approach 2 (Class with Function Pointer) “+” Can wrap a C-style function for C++ Callback … Read more
Functions and function references (i.e. id-expressions of those types) decay into function pointers almost immediately, so the expressions func and f_ref actually become function pointers in your case. You can also call (***func)(5) and (******f_ref)(6) if you like. It may be preferable to use function references in cases where you want the &-operator to work … Read more
This is just a quirk of C. There’s no other reason but the C standard just says that dereferencing or taking the address of a function just evaluates to a pointer to that function, and dereferencing a function pointer just evaluates back to the function pointer. This behavior is (thus obviously) very different from how … Read more
You need a page with write execute permissions. See mmap(2) and mprotect(2) if you are under unix. You shouldn’t do it using malloc. Also, read what the others said, you can only run raw machine code using your loader. If you try to run an ELF header it will probably segfault all the same. Regarding … Read more
In C, there’s no such thing as a function being const or otherwise, so a pointer to a const function is meaningless (shouldn’t compile, though I haven’t checked with any particular compiler). Note that although it’s different, you can have a const pointer to a function, a pointer to function returning const, etc. Essentially everything … Read more
The problem with Fn() is that you can call it multiple times. If you moved out of a captured value, that value would not be available anymore at the next call. You need a FnOnce() to make sure calling the closure also moves out of it, so it’s gone and can’t be called again. There’s … Read more
You have to use auto using fp = auto (*)(int) -> int; typedef auto (*fp)(int) -> int; // alternatively Trailing return type syntax means you put the auto before the function name to indicate that the return type follows (or in the case of c++14, should be deduced). For function pointers, the same rule applies … Read more
In the most normal situation, you can pretty much think of struct A { int i; int foo() { return i; } }; A a; a.foo(); as struct A { int i; }; int A_foo( A* this ) { return this->i; }; A a; A_foo(&a); (Starting to look like C, right?) So you would think … Read more
From the error message, it looks like you’re not allowed to take the address of a parenthesized expression. It’s suggesting that you rewrite fPtr = &(myfoo::foo); // main.cpp:14 to fPtr = &myfoo::foo; This is due to a portion of the spec (ยง5.3.1/3) that reads A pointer to member is only formed when an explicit & … Read more
Here’s one way: int f_real_name(void) { … } #define f f_real_name int g(void) { // call f() } #undef f // calling f() now won’t work Another way, if you can guarantee that f() and g() are the only functions in the file, is to declare f() as static. EDIT: Another macro trick to cause … Read more