How to check if DllCall will work before calling a function

[DCCD]

Hi everybody, To give you an idea, take a look at this simple example of a message box using DllCall function.

$result = DllCall("user32.dll", "int", "MessageBox", "hwnd", 0, "str", "Some text", "str", "Some title", "int", 0)

The question is how to check if DllCall will work before the message box appear?

Thanks & any help would be greatly appreciated..

[Melba23]

DCCD,

Are you trying to see if a dll is present on the machine and ready to use? Perhaps you could make a hidden call to the same dll earlier in the script and see if you get an error response.

M23

[DCCD]

@Melba23, thanks a lot.

let's say i have another Dll has a func that i'd like to use, unfortunately if i call that func and it is being used by another process caused an unexpected error.

Actually the DllCall return value has a lot of helpful information about the error but unfortunately too late!.

About the hidden call, I tried hard to understand that but no luck! what do you mean by the hidden call?

Thanks again..

[Melba23]

DCCD,

I came up with the "hidden call" idea because I thought you were checking for the availabilty of the DLL in general, not just a single function. The idea was that you would just use a simple call to the DLL with no visible effect on your script to see if it returned correctly.

As to your actual requirement to check if a specific function is in use - I am afraid I have no idea. But if it is critical, why not put the call into a loop like this pseudo-code:

start loop
    call dll
    if not error exitloop
    sleep
reloop
if we get here then the call succeeded

Then you will keep calling until your call is successful.. You may want to add a loop counter and abandon the call if yo get too many failures.

Any help?

M23

[trancexx]

let's say i have another Dll has a func that i'd like to use, unfortunately if i call that func and it is being used by another process caused an unexpected error.

That's nonsense.

DllCall() is advanced AutoIt feature for advanced users. The fact that you have managed to construct quoted sentence means you shouldn't be using DllCall() yet. Learn more.

As for DLL availability (check even), use DllOpen() function.

[jchd]

Did you create the offending DLL yourself?

If yes, care to show us the full code/data of the DLL function you invoke?

If not, which DLL are you talking about and why is it built in such a wrong way that it misbehaves?

[DCCD]

That's nonsense.

DllCall() is advanced AutoIt feature for advanced users. The fact that you have managed to construct quoted sentence means you shouldn't be using DllCall() yet. Learn more.

As for DLL availability (check even), use DllOpen() function.

Do i really need to use DllOpen() function, to check a specific function?, i don't think so..

Did you create the offending DLL yourself?

If yes, care to show us the full code/data of the DLL function you invoke?

If not, which DLL are you talking about and why is it built in such a wrong way that it misbehaves?

Actually no, it's not mine, there's nothing wrong with the Dll file, it's simple as my first

How to get some information or check if MessageBox function exists before the message box appear?

DllCall("user32.dll", "int", "MessageBox", "hwnd", 0, "str", "Some text", "str", "Some title", "int", 0)

@trancexx & @jchd, Thank You, all of you

[MilesAhead]

See the functions _WinAPI_LoadLibrary() and _WinAPI_GetProcAddress()

If you can get the address in the DLL of the procedure, chances are it exists in the DLL.

As far as some other program already having a function in use, DLL code is shared but the data is exclusive to each process (aside from specifically created shared data segments etc..)

Unless you are manipulating some hardware or have a locked file, it shouldn't matter if some program is using a function in a DLL. Windows calls are almost all in DLLs and many processes use them all the time.

Edited April 1, 2012 by MilesAhead