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From: lynch@cerc.utexas.edu (Tom Lynch)
Newsgroups: comp.lang.c++
Subject: Re: Why use reference type over pointer type?
Summary: can use on left side of assignment
Keywords: reference &
Message-ID: <1990Aug4.030723.25637@cerc.utexas.edu>
Date: 4 Aug 90 03:07:23 GMT
References: <1676@dinl.mmc.UUCP> <5720@darkstar.ucsc.edu> <21810@lute.com>
Sender: Tom  Lynch
Followup-To: lynch@cerc.utexas.edu
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Organization: University of Texas at Austin
Lines: 57

The one situation I have found where a reference is necessary is
when returning an lvalue to the left side of an assignment.

say I have the class:
      
#include <stream.h>
      class safe_int_array{
           int *data;
           int max_dex;
         public:
           safe_int_array( int size ){ 
                data = new int[size];
                max_dex = size - 1;
           }

           int & operator[](int index){
                 if( index < 0 || index > max_dex ){
                     cerr << "illegal array access \n";
                     exit(1);
                 }else
                     return data[index];
            }
       };/*end class*/


The safe_int_array may be assigned to:

     main(){

           safe_int_array x(7);
           for(int i = 0; i < 7; i++){  //initialize the array
             x[i] = i;
           }
           for( i = 0; i < 7; i++){ //prints: 0123456
             cout << x[i];
           }
           cout << "\n";
    }
       
        
Safe arrays should interest students.  However, returning references
can be very dangerous.  Returning a reference to a local variable can
go unnoticed.  We played with this
and found that the free-ed storage that holds the old subroutines 
local variables will keep the old value until an expression is 
evaluated or another function is called.  By our experience, this is 
the kind of bug which beginners have a very difficult time finding.
It is also hard to explain: "a references is not a pointer but it is..."

I think it is easier to keep track of the C pointer notation in C++
programs; although because references require less typing they
are nice to use :-) :-).

Tom Lynch                           Nothing is absolute.
lynch@cerc.utexas.edu