API Calls without Declare Statements

Posted on 2003-03-04
Medium Priority
Last Modified: 2010-04-07
I just stumbled across this VB Class Module on freevbcode.com, its based on info from vbdotcom.com.  It maked use of a handful of API calls to make a class that can be used to call basicly any API.  I have several questions:
1. Are there any performance issues involved in doing things this way?
2. Are there stability issues?
3. Do this make debuggin any harder?  (It seems to handle "Entry Point" errors pretty well.)
4. It uses a ParamArray to to pass in the Params used by the API call.  How are ParamArrays handled by VB?  Are all of the elements typed as Variants?
5. According to the description on freevbcode.com this class makes it possible to call some previously uncallable functions.  This sound right?

Here is the link to the code:

I am looking for hard answers here, not "I think so"'s or "if i recall correctly"'s or even the coveted "should be".

If answers are given to different questions by different poeple then I will divide up the points as evenly as possible.  That works out to about 40 points a question.
Question by:Da_Weasel
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LVL 28

Accepted Solution

AzraSound earned 800 total points
ID: 8066523
1) I imagine performance issues would be negligible.  Under the covers, Visual Basic calls LoadLibrary on DLLs you have declared at design time and shuffles the memory around to pass in the required parameters

2) Again, I think what you see with the above code is just the low level implementation of what VB is doing anyways

3) I doubt it, except for the issue I will mention at the end

4) Yes

5) Uncallable exported functions of DLLs?  I don't know about that.  How the class works in and of itself, yes.  I believe there is some very interesting "hack-like" code in that class that allows you to pull this off from VB.

The only issue is the one of [out] parameters of any dll.  The above will successfully return the value the function returns, if any.  However, some functions require you pass in a variable that gets filled with information in the DLL function call.  Getting at these values is a trick that the above class doesn't take into consideration, I don't believe.  It would require keeping track of the memory addresses of those variables when passed into the function, and pulling their values back in afterwards.

Author Comment

ID: 8066792
wonderful...I am emailing the author of the code now to ask them about the ByRef params now....will post any info I get from them.

AzraSound: Good answers, I was kinda interested in the 'hack-like' code too.  Looks like the author used API calls to manipulate stacks to emulate ASM in VB.  Thats about as hardcore as you can get with VB IMHO.
LVL 28

Expert Comment

ID: 8066840
The author of that code (expert name 'Ark' here at EE) is notorious for doing the "impossible" from VB.

Author Comment

ID: 8356674
sorry it took so long to award points, havn't visited the site in a while.....

Thanks for the help!

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