What is the difference between the .* and ->* operators?, C++ FAQ

C++ FAQ / Section 33 / FAQ 33.9

Section 33:

33.1	Is the type of "pointer-to-member-function" different from "pointer-to-function"?
33.2	How do I pass a pointer-to-member-function to a signal handler, X event callback, system call that starts a thread/task, etc?
33.3	Why do I keep getting compile errors (type mismatch) when I try to use a member function as an interrupt service routine?
33.4	Why am I having trouble taking the address of a C++ function?
33.5	How can I avoid syntax errors when creating pointers to members?
33.6	How can I avoid syntax errors when calling a member function using a pointer-to-member-function?
33.7	How do I create and use an array of pointer-to-member-function?
33.8	How do I declare a pointer-to-member-function that points to a `const` member function?
33.9	What is the difference between the `.` and `->` operators?
33.10	Can I convert a pointer-to-member-function to a `void*`?
33.11	Can I convert a pointer-to-function to a `void*`?
33.12	I need something like function-pointers, but with more flexibility and/or thread-safety; is there another way?
33.13	What the heck is a functionoid, and why would I use one?
33.14	Can you make functionoids faster than normal function calls?
33.15	What's the difference between a functionoid and a functor?

[33.9] What is the difference between the .* and ->* operators?

You won't need to understand this if you use a macro for member-function-pointer calls. Oh yea, please use a macro in this case. And did I mention that you should use a macro in this case??!?

But if you really want to avoid the macro, sigh, groan, okay, here it is: use .* when the left-hand argument is a reference to an object, and ->* when it is a pointer to an object.

For example:

class Fred { ... };

typedef  int (Fred::*FredMemFn)(int i, double d);  // use a typedef!!! please!!!

void sample(Fred x, Fred& y, Fred* z, FredMemFn func)
{
  x.*func(42, 3.14);
  y.*func(42, 3.14);
  z->*func(42, 3.14);
}

BUT please consider using a macro instead:

void sample(Fred x, Fred& y, Fred* z, FredMemFn func)
{
  CALL_MEMBER_FN(x,func)(42, 3.14);
  CALL_MEMBER_FN(y,func)(42, 3.14);
  CALL_MEMBER_FN(*z,func)(42, 3.14);
}

As discussed earlier, real-world invocations are often much more complicated than the simple ones here, so using a macro will typically improve your code's writability and readability.