From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ross Alexander <rossa@stimpy.math.auckland.ac.nz>
To: egcs@cygnus.com
Subject: ANSI vs Cfront binding
Date: Mon, 01 Dec 1997 13:23:00 -0000
Message-id: <199712012122.KAA31271@stimpy.math.auckland.ac.nz>
X-SW-Source: 1997-12/msg00061.html

A friend of mine showed me this piece of code.  I was interesting on
any comments people had and what should be expected in the future
(with respect to ANSI/ISO compliance).

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// Demonstration of difference between ANSI and Cfront rules
// for binding references.  Program prints "Cfront" when compiled
// with Cfront rules, and "ANSI" when compiled by ANSI rules.

#include <iostream.h>

char x, y;

char *global_ptr;

void Test( const char *const &ref ) {
    // Caller initialized ref to global_ptr, possible via a temporary.  
    // Now change the value of global_ptr.
    global_ptr = &y; 

    if( ref==&x ) {
        // Referenced pointer did not change - must be a temporary.
        cout << "ANSI\n";
    }
    if( ref==&y ) {
        // Referenced pointer changed -- must be directly bound.
        cout << "Cfront\n";
    } 
}

main() {
    global_ptr = &x;

    // Under Cfront rules, the formal parameter ref is bound directly to 
    // global_ptr.  Under ANSI rules, the formal parameter ref is bound
    // to a temporary copy of global_ptr.  Why the temporary?  Because
    // direct binding is allowed [dcl.init.ref] only if the formal and 
    // actual are "reference compatible".  The ANSI rules allow only
    // top-level changes in qualifiers for making lvalues reference compatible.
    
    // No temporary would be generated if the 2nd-level qualifiers were changed
    // to match.  I.e., if global_ptr were of type (const char *) or 
    // ref were of type (char *const &).

    Test( global_ptr );
}