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Re: Conceptual Patch - Handle wrapper class

From: Oto BREZINA <otik_at_printflow.eu>
Date: Sat, 12 Mar 2011 15:00:38 +0100

>> If no: would be better to use NULL (0) as Invalid handler.
> not really. Some APIs return INVALID_HANDLE_VALUE in case of an error,
> so with those we have to check for that value and not 0.
There is one half on APIs returning NULL and half returns
INVALID_HANDLE_VALUE in case of error. In any case you have to check the
other value and set one you choice to be use in "Is INVALID?" check.

>> It may simplify test for invalid handle a bit, also bValid attribute may
>> be removed from class.
>> As I understand INVALID_HANDLER_VALUE is for compatibily with win16 API.
> I don't know about that. AFAIK even current APIs still return
> INVALID_HANDLE_VALUE instead of 0 for errors. I think this isn't an
> issue with compatibility but depends on the API, i.e. which dev team is
> responsible for the API and to which part of the OS it belongs.
Have examples if WinAPI (one we talk about here) method addes in Win32
with error value not NULL ?
I just read some articels about NULL vs. INVALID_HANDLER_VALUE and
author states that all new (not existing in WIN16) methods are NULL on
> If you use CloseHandle() with an invalid handle, an exception is thrown.
> If you run the app under a debugger, it will catch that exception. With
> no debugger, nothing will happen because the exception is caught
> automatically.
> So we really have to make sure to not call CloseHandle() with invalid
> handles because the exceptions make debugging a real nightmare.
That's reason why I tried to use it. Now you have to check docs, what is
error handle returned and add some code to change it if needed. In your
Maybe some function may do a job.
/** return handle it or INVALID_HANDLER_VALUE if handle seems be invalid
HANDLE SetNullAsInvalid(HANDLE h) {
     if (h==NULL)
         return INVALID_HANDLER_VALUE;
     return h;
If fact this solution is more for edge cases that for normal flow.
> While I usually like helper classes, I don't think this would help with
> readability. I kind of like to use 'plain' checks for handle values
> because it's easier to read and also easier to debug.
If it don't help in readability maybe methods names are not right ...
Of corse if you work without it for years (and you catch all pittails),
changing way is not easy.
> Stefan

Oto BREZINA, Printflow s.r.o., EU
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Received on 2011-03-12 15:01:22 CET

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