Just traced down one of those stupid typo errors to find that RegisterClassEx errors when AX is zero - I have assumed MSDN means EAX equal zero is an error: WTF, MS - thanks for wasting 30 minutes of my life.

(Maybe someone else has other pitfalls to note?)

WinDef.h:


Considering that, why do you think it is a typo error from MSDN?

Ignorantly, I didn't think of looking at the return type and assumed the return was in EAX. In this instance I wasn't using the return value. Ultimately, the error is with me because I just started adding API error checking to my code. Then I assumed it was working because of the error checking! Guess it's slightly better than just assuming success on all API functions, lol.

Congratulations

Yeah, using C docs for Asm can sometimes cause problems like this. I probably wouldn't notice this one too :/

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The upper word of EAX is not zero on my Windows when this API fails. Yet, the lower word is zero. YWMV (your windows may vary).

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asmcoder: Don't type bullshit if you don't know. Functions that return WORD return in AX, and functions that return BYTE return in AL.

Irrelevant. Code properly or suffer breakage. Just because flawed code works on one windows version is no excuse to keep flawed code. (Not meant as an insult to bitRAKE, I'd probably have missed such a subtle thing for quite a while too).

Thank you for pointing this out. Although this has not yet bite me, I will be more carefull when checking what a function returns.

Altough, a good design should have some consistence. Guess Windows is not a good example of a good design.

The NT kernel is an example of decent design, the WIN32 API less so (largely because of it's WIN16 legacy). But keep in mind that the API was written with C programmers and not assembly programmers in mind - thus you don't get exact lists of what an API changes and what it doesn't, only the general "expect these registers to be modified, and you're guaranteed those registers aren't".

This also means that if only a byte or a word is returned, you should only look at that part of EAX, and consider the rest to be undefined. Use movsx/movzx if this is too horrible for you

Also have you noticed that some Win builds treat BOOL as al (1 byte) other as eax (4 bytes)? As i remember i stumbled this.