How do I create and use an array of pointer-to-member-function?, C++ FAQ

C++ FAQ / Section 33 / FAQ 33.7

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?

[33.7] How do I create and use an array of pointer-to-member-function?

Use both the typedef and the #define macro described earlier, and you're 90% done.

Step 1: create a typedef:

class Fred {
public:
  int f(char x, float y);
  int g(char x, float y);
  int h(char x, float y);
  int i(char x, float y);
  ...
};

// FredMemFn points to a member of Fred that takes (char,float)
typedef  int (Fred::*FredMemFn)(char x, float y);

Step 2: create a #define macro:

#define CALL_MEMBER_FN(object,ptrToMember)  ((object).*(ptrToMember))

Now your array of pointers-to-member-functions is straightforward:

FredMemFn a[] = { &Fred::f, &Fred::g, &Fred::h, &Fred::i };

And your usage of one of the member function pointers is also straightforward:

void userCode(Fred& fred, int memFnNum)
{
  // Assume memFnNum is between 0 and 3 inclusive:
  CALL_MEMBER_FN(fred, a[memFnNum]) ('x', 3.14);
}

Note: #define macros are evil in 4 different ways: evil#1, evil#2, evil#3, and evil#4. But they're still useful sometimes. Feel ashamed, feel guilty, but when an evil construct like a macro improves your software, use it.