It works because the Standard says that’s how it should happen. I did some tests with GCC, and it turns out for virtual functions, GCC stores the virtual table offset of the function in question, in bytes. struct A { virtual void f() { } virtual void g() { } }; int main() { union … Read more
In c++17, with the addition of auto in template arguments (P0127), I think you can now do: template<auto value> struct MyStruct {}; template<typename Class, typename Result, Result Class::* value> struct MyStruct<value> { // add members using Class, Result, and value here using containing_type = Class; }; typename MyStruct<&Something::theotherthing>::containing_type x = Something();
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 (§5.3.1/3) that reads A pointer to member is only formed when an explicit & … Read more
The syntax is wrong. A member pointer is a different type category from a ordinary pointer. The member pointer will have to be used together with an object of its class: class A { public: int f(); int (A::*x)(); // <- declare by saying what class it is a pointer to }; int A::f() { … Read more
Read this for detail : // 1 define a function pointer and initialize to NULL int (TMyClass::*pt2ConstMember)(float, char, char) const = NULL; // C++ class TMyClass { public: int DoIt(float a, char b, char c){ cout << “TMyClass::DoIt”<< endl; return a+b+c;}; int DoMore(float a, char b, char c) const { cout << “TMyClass::DoMore” << endl; … Read more
Currently there is no standard way of doing this in C++ although the information must be available somewhere. Otherwise, how could the program call the function? However, GCC provides an extension that allows us to retrieve the address of a virtual function: void (A::*mfp)() = &A::func; printf(“address: %p”, (void*)(b->*mfp)); …assuming the member function has the … Read more
C++03 std, §4.11 2 Pointer to member conversions: An rvalue of type “pointer to member of B of type cv T,” where B is a class type, can be converted to an rvalue of type “pointer to member of D of type cv T,” where D is a derived class (clause 10) of B. If … Read more
In the standard (e.g. N3337 – not the latest but fine for this) there is a note at the end of section 8.3.3.3 that reads: [ Note: See also 5.3 and 5.5. The type “pointer to member” is distinct from the type “pointer”, that is, a pointer to member is declared only by the pointer … Read more
ns::B::* is a pointer-to-member-variable of B. Then ns::A* is its type. So the whole declaration means pointer-to-member-variable of B of type ns::A*