From mboxrd@z Thu Jan  1 00:00:00 1970
From: "swe sd" <ccwork@hotmail.com>
To: jay.krell@cornell.edu
Cc: cygwin@sourceware.cygnus.com
Subject: Re: problem in C++ pointer
Date: Sat, 11 Mar 2000 21:20:00 -0000
Message-id: <20000312052029.47987.qmail@hotmail.com>
X-SW-Source: 2000-03/msg00250.html

  I do not agree. I execute the same program on a UNIX station with gcc 
compiler and it works fine ... ie the output of line 7 is
same as the output of line 9.

>From: "Jay Krell" <jay.krell@cornell.edu>
>To: "swe sd" <ccwork@hotmail.com>, <cygwin@sourceware.cygnus.com>
>Subject: Re: problem in C++ pointer
>Date: Sat, 11 Mar 2000 16:31:28 -0800
>
>Your code might be triggering undefined behavior in C++, because of the
>++X[0] in the same statement where you otherwise read X[0]. Definitely
>something like
>printf("%d%d", X[0], ++X[0]);
>is undefined but I've read something along the lines that when the
>operator's are actually overloaded, function calls, that the order of
>evaluation becomes defined..
>
> >     line 9:    cout<<A[0]<<" "<<&A<<" "<<&A[0]<<endl
> >     line 10:       <<*X<<endl
> >     line 11:       <<*X+5<<endl
> >     line 12:       <<*X<<" "<<A[0]<<endl
> >     line 13:       <<5+X[0]<<endl
> >     line 14:       <<( X[0]==0 ? "X[0]=0" : "X[0]!=0")<<endl
> >     line 15:       <<++X[0]<<endl
>
>something like, skipping endl.
>cout.<<(A[0]).<<(" ").<<(&A).<<(" ").<<(&A[0]).<<(*X).<<(*X+5).<<(*X).<<("
>").<<A[0].<<(5+X[0]).<<(( X[0]==0 ? "X[0]=0" : "X[0]!=0")).<<(++X[0]);
>
>  - Jay
>
>-----Original Message-----
>From: swe sd <ccwork@hotmail.com>
>To: cygwin@sourceware.cygnus.com <cygwin@sourceware.cygnus.com>
>Date: Saturday, March 11, 2000 9:31 AM
>Subject: B20: problem in C++ pointer
>
>
> >   I compiled the following program (attachment test.cc):
> >     line 1:  #include <iostream>
> >     line 2:  void main()
> >     line 3:  { const int size=10;
> >     line 4:    int A[size];
> >     line 5:    int *X=NULL, i;
> >     line 6:    for (i=0;i<size;i++) A[i]=i;
> >     line 7:    cout<<A[0]<<" "<<&A<<" "<<&A[0]<<endl;
> >     line 8:    X=A;
> >     line 9:    cout<<A[0]<<" "<<&A<<" "<<&A[0]<<endl
> >     line 10:       <<*X<<endl
> >     line 11:       <<*X+5<<endl
> >     line 12:       <<*X<<" "<<A[0]<<endl
> >     line 13:       <<5+X[0]<<endl
> >     line 14:       <<( X[0]==0 ? "X[0]=0" : "X[0]!=0")<<endl
> >     line 15:       <<++X[0]<<endl
> >     line 16: }
> >    and executing it gives output:
> >           $./a.out
> >           0 0x259fd7c 0x259fd7c
> >           1 0x259fd7c 0x259fd7c
> >           1
> >           6
> >           1 1
> >           6
> >           X[0]!=0
> >           1
> >    Obviously, the output of line 9 is different from line 7 which > 
> >should be the same indeed. Is there anything wrong ? Thanks.

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