Mail Archives: cygwin/2000/03/11/19:33:46
Darn, sent that before finishing..
>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]);
something like, skipping endl.
cout
.print(A[0])
.print(" ")
.print(&A)
.print(" ")
.print(&A[0])
.print(*X)
.print(*X+5)
.print(*X)
.print(" ")
.printA[0]
.print(5+X[0])
.print(( X[0]==0 ? "X[0]=0" : "X[0]!=0"))
.print(++X[0]);
whether or not the left of the dots is supposed to be evaluated before the
right and the parameters to "print", I'm not sure. See "sequence point" in
the standard..
- Jay
-----Original Message-----
From: Jay Krell <jay DOT krell AT cornell DOT edu>
To: swe sd <ccwork AT hotmail DOT com>; cygwin AT sourceware DOT cygnus DOT com
<cygwin AT sourceware DOT cygnus DOT com>
Date: Saturday, March 11, 2000 4:31 PM
Subject: Re: problem in C++ pointer
>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
>operators 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 AT hotmail DOT com>
>To: cygwin AT sourceware DOT cygnus DOT com <cygwin AT sourceware DOT cygnus DOT 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.
>>
>>______________________________________________________
>>Get Your Private, Free Email at http://www.hotmail.com
>>
>
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