vc 6.0 's bug?????

[fisker0303]

In vc 6.0:

#include <iostream>
using namespace std;

int main()
{
int a = 10;
int b = 20;
a = (a + b) - (b = a);
cout << "a=" << a << ",b=" << b << endl;
return 0;
}

Release output : a=20,b=10
Debug output: a=10,b=10

why?

 

[Ian Collins]

In vc 6.0:

#include <iostream>

Wrong language, you want the C++ group down the hall.

 

[Vladimir Oka]

(e-mail address removed) opined:

In vc 6.0:

#include <iostream>
using namespace std;

Got the wrong address. This is comp.lang.c.

Followups-to comp.lang.c++ set...

 

[CBFalconer]

In vc 6.0:

#include <iostream>
using namespace std;

int main()
{
int a = 10;
int b = 20;
a = (a + b) - (b = a);
cout << "a=" << a << ",b=" << b << endl;
return 0;
}

Release output : a=20,b=10
Debug output: a=10,b=10

why?

Because, on close examination of the newsgroups name, you might
detect the absence of the '++' portion. To an eagle eyed
programmer of your mental capability this might carry connotations
indicating that C++ is not the subject under discussion. Such an
alert usenet user might then decide to use comp.lang.c++, and would
still be wrong. VC of any vintage is a proprietary compiler, and
probably bad (considering the origin), but is not on topic in any
newsgroup that discusses a pure language as defined by standards.

--
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More details at: <http://cfaj.freeshell.org/google/>
Also see <http://www.safalra.com/special/googlegroupsreply/>

 

[Kenneth Brody]

In vc 6.0:

#include <iostream>
using namespace std;

int main()
{
int a = 10;
int b = 20;
a = (a + b) - (b = a);
cout << "a=" << a << ",b=" << b << endl;
return 0;
}

Release output : a=20,b=10
Debug output: a=10,b=10

why?

As has been pointed out, this is comp.lang.c, not comp.lang.c++.

However, noting that this is a C answer, and may be 100% wrong for
a C++ program....

a = (a + b) - (b = a);

I believe that this invokes "undefined behavior", because you both
use and modify "b" between sequence points. There is no guarantee
that the "b" in "a+b" will be evaluated before the "b" in "b=a".
You may get the equivalent of:

a = (10 + 20) - (10);
or
a = (10 + 10) - (10);
or
system("format c:");

The fact that you get what appears to be the first behavior for
"release" and the second for "debug" is perfectly acceptable, as
"undefined behavior" means _anything_ can happen.

--
+-------------------------+--------------------+-----------------------------+
| Kenneth J. Brody | www.hvcomputer.com | |
| kenbrody/at\spamcop.net | www.fptech.com | #include <std_disclaimer.h> |
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Don't e-mail me at: <mailto:[email protected]>