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 [thread overview]
Message-ID: <20000312052029.47987.qmail@hotmail.com> (raw)
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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next reply other threads:[~2000-03-11 21:20 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2000-03-11 21:20 swe sd [this message]
-- strict thread matches above, loose matches on Subject: below --
2000-03-17 13:26 Heribert Dahms
2000-03-17 13:15 Jay Krell
2000-03-17 9:48 Jay Krell
2000-03-16 8:39 James Stern
2000-03-13 2:07 Jay Krell
2000-03-13 1:54 Bernard Dautrevaux
2000-03-12 19:51 Jay Krell
2000-03-12 7:52 swe sd
2000-03-12 0:06 Jay Krell
2000-03-11 16:33 Jay Krell
2000-03-11 16:29 Jay Krell
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