Pointertomember

Pointer-to-member, sometimes written as pointer-to-member or pointertomember, is a C++ language feature that enables references to non-static members of a class, either data members or member functions. It encodes the location of a member within a class and requires an object (or a pointer to one) to be used.

Data member pointers are declared as type ClassName::* and initialized with the address of a member, for example int ClassName::*ptr = &ClassName::field;. Member function pointers are declared with a function type in the class scope, such as void (ClassName::*pmf)(int) = &ClassName::method;. These pointers are not ordinary pointers to functions or data; they refer to a member relative to a specific class.

Accessing a data member through a pointer-to-member uses the object and the appropriate operator: obj.*ptr or objPtr->*ptr. You can read or assign the member via these expressions. Invoking a member function through a pointer-to-member likewise requires an object: (obj.*pmf)(arg) or (objPtr->*pmf)(arg).

Pointer-to-member enables dynamic or generic programming patterns, such as storing a set of member pointers in a container and invoking them on different objects at runtime, implementing callbacks, event handling, or reflection-like mechanisms. They are particularly useful when the exact member to access is not known until runtime.

Limitations include the need for a concrete object to apply the pointer, and the fact that pointers to data members and pointers to member functions are distinct and cannot be treated as regular function or data pointers. The syntax and semantics are specific to C++ and some related languages.