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From: idf@cs.bham.ac.uk (Ian Fitchet <FitchetI>)
Newsgroups: comp.lang.c++
Subject: Pointers to Member Functions
Message-ID: <1369@christopher-robin.cs.bham.ac.uk>
Date: 5 Dec 90 16:40:37 GMT
Organization: University of Birmingham, England
Lines: 57


 I came across a problem while trying to explain pointers to functions
from a C perspective in a C++ tutorial. This failed so I looked it up
in a book which said that the following code should be valid.

#include <stream.h>
class foo {
  int a;
public:
  foo() { a = 1; }
  void print() { cout << a << "\n"; }
  void bar() { a = 3; }
};
main()
{
  void (foo::*ptr2bar)() = &foo::bar;
  foo bletch;
  
  cout << "Initially a = " ;
  bletch.print();
  bletch.(*ptr2bar)();
  cout << "Finally a = ";
  bletch.print();
}

 The Sun C++ compiler (CC -v prints out "Sun C++ 2.0 FCS - 10/20/89")
does the following:

%cd /mbhome/staff/idf/src/cc/
%CC -o foo q.c
%CC  q.c:
%"q.c", line 36: error: syntax error
%1 error
%cc   -o /mbhome/staff/idf/src/cc/foo -c -I/usr/CC/incl 
%
%Compilation exited abnormally with code 1 at Wed Dec  5 16:03:08

 ie a syntax error on the call.

 g++ version 1.37.2 beta (based on GCC 1.37) does the following:

%cd /mbhome/staff/idf/src/cc/
%g++ -o foo q.c
%q.c: In function int main ():
%q.c:30: parse error before `*'
%
%Compilation exited abnormally with code 1 at Wed Dec  5 16:32:09

 ie gives a parse error on the declaration of ptr2bar
 void (foo::*ptr2bar)() = &foo::bar;

 Is it me, or are the compilers to blame?

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Ian Fitchet                               | "Have you heard the one about the
FitchetI@uk.ac.bham.cs                    | orangutan and the pomegranate?"
FitchetI%cs.bham.ac.uk@nsfnet-relay.ac.uk | 	- Gerald the Gorilla (NTNO'CN)


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