DLL - Call results improvement?

[kpeters58]

Hi all,

just built a DLL as per code below. When setting

Code: Select all

#BUILD_DLL = #False

and thus testing it, I get the DLL's Messagerequester displaying my message just fine. I do, however, get a '0' as Result of CallFunction, indicating a failure (as per PB Help) and the Debug window pops up.

Help file:

Return value

Returns the return-value of the called function or zero if the library does not contain a function with the given name.

So to me this looks like the called function returns '0' (as per help) - now we have a situation where we don't know if the called proc failed (in my case we see the requester, so we know it's ok - but in other cases we will be in the dark).

I could give it a dummy return value <> '0' so it becomes testable again - or Fred could resolve this ambiguity in code... or at least the help could be updated to point this potential pitfall out to unsuspecting users (like me today)...

Is this a valid assessment or am I missing something here?

Code: Select all

#BUILD_DLL = #False

CompilerIf #BUILD_DLL 

  ProcedureDLL DLLRequester(Msg$)
    MessageRequester("DLL Requester", Msg$)
  EndProcedure

CompilerElse
  EnableExplicit
  
  #LibHandle = 1
  Define Result
  
  If OpenLibrary(#LibHandle, "InstallHelper.dll") ;;; Or OpenLibrary(0, "InstallHelper.so")
    Result = CallFunction(#LibHandle, "DLLRequester", @"I've got to get a message to you ...")  
    If Result = 0
      Debug "Call function failed"
    EndIf
  Else
    Debug "Lib open failed"
  EndIf
    
CompilerEndIf

[mk-soft]

Check with GetFunction(...) or the result of function have never #NULL

[kpeters58]

Check with GetFunction(...) or the result of function have never #NULL

True, that's a fourth option - albeit an extra function call.

I still feel that the help for CallProcedure/CallCProcedure should include a warning along the lines:

OLD

Return value
Returns the return-value of the called function or zero if the library does not contain a function with the given name.

NEW

Return value
Returns the return-value (which may be zero) of the called function or zero if the library does not contain a function with the given name.
Use GetFunction() to test for the existence of a DLL function.

[HeX0R]

CallFunction is outdated anyway, I didn't use that anymore since years.
Prototypes should be used, they are much more flexible and powerful.
Then you will see via GetFunction if a procedure exists or not.