Re: c++/1920

[Eric Blake <ebb9@email.byu.edu>]

The following reply was made to PR c++/1920; it has been noted by GNATS.

From: Eric Blake <ebb9@email.byu.edu>
To: mdejong@redhat.com, gcc-gnats@gcc.gnu.org, nobody@gcc.gnu.org
Cc:  
Subject: Re: c++/1920
Date: Fri, 09 Feb 2001 15:51:35 -0700

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view&pr=1920&database=gcc
 
 Actually, it looks like this bug should be recategorized as
 accepts-illegal.  Consider this variation:
 
 #include <stdio.h>
 void foo(unsigned &bar)
 {
     bar = 1;
 }
 int main()
 {
     unsigned a = 0;
     foo((unsigned) a);
     if (a == 1)
         printf("OK\n");
     else {
         printf("a = %d, expeceted 1", a);
         return 1;
     }
     return 0;
 }
 
 $ g++ -o foo foo.cc
 foo.cc: In function `int main()':
 foo.cc:9: initialization of non-const reference type `unsigned int &'
 foo.cc:9: from rvalue of type `unsigned int'
 foo.cc:3: in passing argument 1 of `foo(unsigned int &)'
 
 Therefore, the fact that changing the declaration of a from unsigned to
 int allows the compiler to complete without warning or error is the true
 bug.  In line 10, (unsigned) a is an rvalue, which cannot be assigned to
 the non-const unsigned & of foo().  The correct cast in this situation
 would be (unsigned &) a, which does work as expected.
 
 -- 
 Eric Blake