Re: Porting from VC6 to VS2005

From:

David Wilkinson <no-reply@effisols.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Sat, 27 Sep 2008 14:22:11 -0400

Message-ID:

<u$sp03MIJHA.4416@TK2MSFTNGP06.phx.gbl>

Ian Semmel wrote:

The trouble is that you can produce program bugs if you make a mistake
making the changes eg I think I did something along these lines trying
to fix the 'for' problem

    int i =23; // I added this line

    for ( int i = 0; somecondition; i++ ) // I meant to take 'int' out
    {
    }

    int b = i;

which compiles fine but didn't give me the desired result.

But yes, it did find real errors in my code. I was defining targets of
thread messages as returning LRESULT instead of void.

I was also indexing a local array out of bounds which the debugger caught.

1. Yes. The for loop scoping is probably the most troublesome (and ubiquitous)
problem when updating. Your original code was illegal, but you made a mistake
updating it. If you hadn't initialized i then "uninitialized variable" might
have saved you. This is why I long ago changed my VC6 code to use the

#define for if(false){} else for

trick. Then you can have legal code that compiles in both VC6 and later.

2. The return value of PostThreadMessage() was actually a breaking change in
MFC. I had to use the preprocessor to get code that would compile both on VC6
and later versions.

3. Array out of bounds was a bug in your code.

I'm not saying that the better compiler and debugger do not find bugs in your
code, rather that they find bugs that can usually be fixed so they work in both
places.

Of course there are some code constructs, especially advanced template ones,
that simply were not supported in VC6. But template code that worked in VC6 can
usually be corrected so it is legal (and still works in VC6).

--
David Wilkinson
Visual C++ MVP