Mail Archives: cygwin/2000/03/12/22:52:22
>I just wonder what is the different between the original code
>(using a single "cout", see test.cc attached) and new code
>(use another cout to print ++X[0], above).
The difference is that there is definitely a "sequence point" at every
semicolon. The effects of code to the left of a semicolon are guaranteed to
be visible before the effects of code to the right of the same semicolon.
int i, j, k;
F(j = i++, k = i++);
is undefined, the parameters can be evaluated in any order even sort of
simultaneously, whereas
j = i++;
k = i++;
F(j, k);
and
k = i++;
j = i++;
F(j, k);
are defined. The first line must be completely executed before the second
line.
> Actually, I tried the original program many time on my PC
>running Cygnus. To remove external factor, I close all other
>program after a re-boot.
I got the same behavior as you, with 2.95.2 to as well. I tried reading the
assembly (gcc -s x.cpp, then look at the file x.s) but it didn't include
commented out C++ source so was too hard to follow.
- Jay
-----Original Message-----
From: swe sd <ccwork AT hotmail DOT com>
To: jay DOT krell AT cornell DOT edu <jay DOT krell AT cornell DOT edu>
Cc: cygwin AT sourceware DOT cygnus DOT com <cygwin AT sourceware DOT cygnus DOT com>
Date: Sunday, March 12, 2000 7:52 AM
Subject: Re: problem in C++ pointer
> First of all, thanks for you kindy answer ...
> I have the last question. I rewrite the program as follow:
> 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: cout<<++X[0]<<endl; //the change here
> line 16: }
> and executing it gives output:
> $./a.out
> 0 0x259fd7c 0x259fd7c
> 0 0x259fd7c 0x259fd7c
> 0
> 5
> 0 0
> 5
> X[0]=0
> 1
> Obviously, it gives the correct answer (line 7 = line 9). I
>just wonder what is the different between the original code (using
>a single "cout", see test.cc attached) and new code (use another
>cout to print ++X[0], above).
> Actually, I tried the original program many time on my PC
>running Cygnus. To remove external factor, I close all other
>program after a re-boot. But the result is still wrong (see last e-mail).
> Then, to test my program is correct or not, I tried it on a
>UNIX SVR with gcc compiler. Then the program works properly.
> So, I just conclude there is some wrong with the cygwin, or
>not as good as gcc. Thanks.
>______________________________________________________
>Get Your Private, Free Email at http://www.hotmail.com
>
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