Re: problem in C++ pointer

["Jay Krell" <jay.krell@cornell.edu>]

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.krell@cornell.edu>
To: swe sd <ccwork@hotmail.com>; cygwin@sourceware.cygnus.com
<cygwin@sourceware.cygnus.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@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.
>>
>>______________________________________________________
>>Get Your Private, Free Email at http://www.hotmail.com
>>
>


--
Want to unsubscribe from this list?
Send a message to cygwin-unsubscribe@sourceware.cygnus.com