Function pointer pointed to a member function

Question

I am just learning function pointer and want to test how it works with member functions. The compilation of the following code fails at where it is marked.

# include <iostream>
# include <stdio.h>
using namespace std ;

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 ) {
    cout << " TMyClass::DoMore " << endl ;
    return a - b + c ;
  }

  int ( TMyClass::*pt2Member ) ( float, char, char ) ;

  int test_function_pointer ( ) {
    this->pt2Member = &TMyClass::DoMore ;
    int result = ( this -> *pt2Member ) ( 12, 'a', 'b' ) ; // wrong!
    // expected unqualified-id before "*" token

    return 0 ;
  }
} ;

int main () {
  TMyClass A ;
  A.test_function_pointer () ; 
  return 0 ;
}

I wonder how to make it work. Thanks!

πάντα ῥεῖ · Accepted Answer · 2016-12-10 12:35:40Z

5

What a difference a space makes:

int result = ( this ->* pt2Member ) ( 12, 'a', 'b' );
                 // ^^^

->* is an operator of its own.

See the fixed demo here please.

answered Dec 10, 2016 at 12:35

πάντα ῥεῖ

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Comments

Tomek · Accepted Answer · 2016-12-10 12:38:02Z

0

This line:

int result = ( this -> *pt2Member ) ( 12, 'a', 'b' ) ; // wrong!

should have been:

int result = ( this ->*pt2Member ) ( 12, 'a', 'b' ) ; // wrong!

->* is an operator and you cannot insert spaces inside it as it splits it into two different operators: -> and *. This is similar to <<, >>, --, ++ which also cannot be split by spaces into two different tokens.

answered Dec 10, 2016 at 12:38

Tomek

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