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I have seen an example. in that example there is a line like x->*y. what is it? ->*. I am new in C++ programming and I don't have much knowledge about operator. Can anybody describe it?

Jason C
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Shell
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    Not hard at all to check: http://en.cppreference.com/w/cpp/language/operator_precedence. Oh, and it isn't part of C. – chris Feb 22 '14 at 06:10
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    It's not one operator. It's the `->` operator followed by the `*` operator. – Barmar Feb 22 '14 at 06:12
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    @Barmar, It sure is in C++, and I don't think you can have that syntax in C. – chris Feb 22 '14 at 06:15
  • @chris I have read that and i found some operator like `->`, `*` and `->*`. So, i am getting confused. Is it combination of two operator `->` and `*` or it just a single operator `->*` (Pointer to member)? – Shell Feb 22 '14 at 06:16
  • @Nimesh, It's a single operator. Those are three separate things. Tons of resources on each of them on Google and in books. – chris Feb 22 '14 at 06:17
  • https://publib.boulder.ibm.com/infocenter/lnxpcomp/v8v101/index.jsp?topic=%2Fcom.ibm.xlcpp8l.doc%2Flanguage%2Fref%2Fcplr034.htm – Barmar Feb 22 '14 at 06:18
  • http://msdn.microsoft.com/en-us/library/k8336763.aspx – Barmar Feb 22 '14 at 06:19
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    @Felix Same with [What are the Pointer-to-Member ->* and .* Operators in C++?](https://stackoverflow.com/questions/6586205/what-are-the-pointer-to-member-and-operators-in-c) Not sure why duplicates get upvoted. –  Feb 22 '14 at 06:29
  • @remyabel the only problem with the answers in these dupes is they're all seemingly centric on pointer to member *functions*, failing to fully cover that the operator is useful for pointer to member *everything*. For some reason member *variables* isn't covered well, and in most cases at-all. No clue why. [**See it live**](http://ideone.com/10wnBm). – WhozCraig Feb 22 '14 at 06:36
  • @FelixKling The link posted by remyabel is earlier. – Jason C Feb 22 '14 at 06:40

2 Answers2

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It's called "pointer to member of pointer" and is one of the "pointer to member" type operators (in addition to .*, "pointer to member of object").

You can use it when you take the address of a member variable or function of a class, then you want to access that variable or call that function on an instance of that class, given a pointer to the instance (like a vanilla data or function pointer, but to a class member).

Here is an example using function pointers:

#include <cstdio>
using namespace std;

class Example {
public:
  Example (int value) : value_(value) { }
  void printa (const char *s) { printf("A %i %s\n", value_, s); }
  void printb (const char *s) { printf("B %i %s\n", value_, s); }
private:
  int value_;
};

// print_member_ptr can point to any member of Example that
// takes const char * and returns void. 
typedef void (Example::* print_member_ptr) (const char *);

int main () {

  print_member_ptr ptr;
  Example x(1), y(2), *p = new Example(3), *q = new Example(4);

  ptr = &Example::printa;
  // .*ptr and ->*ptr will call printa
  (x.*ptr)("hello");
  (y.*ptr)("hello");
  (p->*ptr)("hello");
  (q->*ptr)("hello");

  ptr = &Example::printb;
  // now .*ptr and ->*ptr will call printb
  (x.*ptr)("again");
  (y.*ptr)("again");
  (p->*ptr)("again");
  (q->*ptr)("again");

}

The output is:

A 1 hello
A 2 hello
A 3 hello
A 4 hello
B 1 again
B 2 again
B 3 again
B 4 again

See http://en.cppreference.com/w/cpp/language/operator_member_access for more details.

Jason C
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2

It's a Member pointed to by b of object pointed to by a.

Syntax

a->*b

As member of K 

R &operator ->*(K a, S b);

Outside class definitions

R &K::operator ->*(S b);

See more at Wikipedia.