Runtime DLL loading via macro. Will it work.

[BOB MECHLER]

I have a need to load at runtime specific custom dll's by customer. I used some examples from the forum to get the idea and came up with the following. It works but I'm concerned if there are problems with this method.
Declare and Macro code

DECLARE FUNCTION GET_CHN_PRD(STRING) AS STRING
MACRO CALLDLL1(prm1,prm2,prm3,prm4,prm5)
  'This variable passes a single parameter
  'Other variations would just have prm6,prm7 etc.
  'prm1 root name of dll
  'prm2 function name in dll
  'prm3 return value. can be -1,0,any type of number or string
  'prm4 Number of DLL call in program. If more than 1 dll is called then it may be up to 10 (arbitrary limit)
  'prm5 Variable 1 passed BYREF
  DIM hLibrary???(10)
  DIM pProc???(10)
  'The DLL would be in PBSRC if running at out office and
  'in the program directory at the customer site.
  IF NOT FNSP(CUST_DIR$) THEN
    DLLPATH$ = "J:\PBSRC\TNET\" + CUST_DIR$ + "\"
  ELSE
    DLLPATH$ = ""
  END IF
  DLLNAME$ = prm1
  DLLNAME$ = DLLPATH$ + DLLNAME$ + ".DLL"
  hLibrary???(prm4) = LoadLibrary(BYCOPY DLLNAME$)
  IF hLibrary???(prm4) THEN
    pProc???(prm4) = GetProcAddress(hLibrary???(prm4),prm2)
    IF pProc???(prm4) THEN
      CALL DWORD pProc???(prm4) USING GET_CHN_PRD(prm5) TO prm3
      CALL FreeLibrary(hLibrary???(prm4))
    END IF
  ELSE
    MSGBOX "Required DLL " + DLLNAME$ + " is not present. Aborting program." ,%MB_OK OR %MB_ICONWARNING,"File not found"
    GOTO EJOB
  END IF
END MACRO

PBMAIN code snippet

      IF CTRU THEN 'where CTRU is the customer code
        CALLDLL1("LBCHNPRD","GET_CHN_PRD",CHN_PRD$,1,BYCOPY F1.ACTNR$) 
      END IF

LBCHNPRD is the root of the DLL name
GET_CHN_PRD is the name of the function to call
CHN_PRD$ is the returned value EXPORTED AS STRING
1 is the number of the DLL being called to keep the pointers unique to the DLL being called.
BYCOPY F1.ACTNR$ is the single parameter I'm passing to the DLL.

I'm considering using OPTIONAL and ANY to make the MACRO more generic.

Any comments and/or warnings and/or suggestions are welcome.

Bob Mechler

[BOB MECHLER]

Just noticed I'll probably need to use a macro parameter on the GET_CHN_PRD portion in CALL DWORD.

I had problems when passing params with quotes and without quotes in the macro expansion. Any thoughts there also.

Bob Mechler

[Michael Mattias]

Your FreeLibrary is in the wrong place

IF hLibrary???(prm4) THEN
    pProc???(prm4) = GetProcAddress(hLibrary???(prm4),prm2)
    IF pProc???(prm4) THEN
      CALL DWORD pProc???(prm4) USING GET_CHN_PRD(prm5) TO prm3
      CALL FreeLibrary(hLibrary???(prm4))
    END IF
  ' FreeLibrary belongs here so it's called anytime LoadLibrary succeeded
     ' and not just when the named proc is found in the loaded library.

Re MACRO/parameter/quotes usage: why bother with a MACRO? Just make it a procedure.

[BOB MECHLER]

You're right of course, FreeLibrary should be in the scope of a successful LoadLibrary.

DLL's that are common to all customers, I DECLARE at the beginning of the program. Conditional DLL'S that depend on the modules purchased and/or unique functionality per customer could be numerous and not everyone would have them.

Anytime I see code repeating itself in different functions I tend to think MACRO to generalize it. Implicit run-time linking looked to me like something that could be generalized. That way I could place it once in an include file with all other MACRO's and in our programs a single DECLARE at the top of the program and a single line of code in PBMAIN would be able to call any DLL we write in the furture, handling in a custom directory at the office and in the customer program directory in the field.

I chose a macro because I couldn't figure out how to make a function that could be used to load any dll, get a return value and then unload. The CALL DWORD pProc??? USING requires the name. Also I wanted to delay, in some cases, freeing the libary in the event the call to the DLL was in a loop. Then I would free the libary when ending the program. To free the library later, I would have to use a global array to keep track of the handles of the DLL'S that had been loaded.

How could a function that needs to be able to load at runtime any DLL and call any function within that DLL be written?

Bob Mechler

[Michael Mattias]

How could a function that needs to be able to load at runtime any DLL and call any function within that DLL be written?

DECLARE FUNCTION ProtoType_One (sz AS ASCIIZ) AS LONG 
DECLARE FUNCTION ProtoType_Two (sz AS ASCIIZ, l AS LONG) AS LONG

FUNCTION CallMyFunction (szLib AS ASCIIZ, szProc AS ASCIIZ, OPTIONAL szparam1 AS ASCIIZ, szParam2 AS ASCIIZ.... ) AS LONG

  hLib = LoadLibrary (szLib)
  dwProc = getProcAddress (szProc)

  SELECT CASE szProc
    CASE "FunctionOne" 
       CALL DWORD DwProc USING Prototyope_One (szParam1)  TO iRet
    CASE "FunctionTwo"
       CALL DWORD dwProc USING Prototype_two (szParam1, VAL(szParam2))  TO iRet

    .....
  FreeLibrary  hLib 
  FUNCTION= iRet

MCM

[John Petty]

I am not good at macros but htink you should split the problem into two sections, one which just controls what dll's are loaded and used, the other which gets the data from them. Below is some sample code, note it only allows you to load a dll once and also can return results of any type.

DECLARE FUNCTION GetInfoFromDLL(Reslt AS ANY) AS LONG

FUNCTION OpenCloseCustomDll(DllName AS STRING, DllPath AS STRING, Action AS LONG) AS DWORD
    ' Action = 0 to open, -1 to close
    DIM STATIC DllAdd(0) AS DWORD
    DIM STATIC DllNme(0) AS STRING
    LOCAL x AS LONG
    IF Action THEN
        FOR x = 0 TO UBOUND(DllNme)
            IF DllPath + DllName = DllNme(x) AND DllAdd(x) <> &hFFFFFFFF THEN
                Freelibrary DllNme(x)
                DllAdd(x) = &hFFFFFFFF
                EXIT FOR
                FUNCTION = 0
            END IF
        NEXT
    ELSE
        FOR x = 0 TO UBOUND(DllNme)
            IF DllPath + DllName = DllNme(x) THEN
                IF DllAdd(x) <> &hFFFFFFFF THEN
                    FUNCTION = DllAdd(x)    'already open
                ELSE
                    FUNCTION = 0    'tried before dll does not exist
                END IF
                EXIT FOR
            END IF
        NEXT
        IF x > UBOUND(Dllnme)
            REDIM PRESERVE DllNme(x)
            REDIM PRESERVE DllAdd(x)
            DllAdd(x) = LoadLibray(DllPath + DllName)
            FUNCTION = DllAdd(x)
            IF DllAdd(x) = 0 THEN DllAdd(x) = &HFFFFFFFF
        END IF
    END IF
END FUNCTION

' in your code first check the state of the dll and its existance
ThisDllAdd = OpenCloseCustomDll(NameOfDll, OfficePath, 0)
IF ThisDllAdd THEN
    ProcAdd = GetProcAddress(ThisDllAdd, ProcName)
    IF ProcAdd THEN
        CALL DWORD ProcAdd USING GetInfoFromDll(VariableOfTypeYouExpect) TO Retn
        'retn can give you an error code
        
'at some convenient time you can unload all the dlls that may be there just change the action to -1

John

[BOB MECHLER]

Good clear examples. Thanks.

I'm gonna forget the macro approach. I see now pretty much how I can do it from the examples.

Thanks,

Bob Mechler

[BOB MECHLER]

This code fits my needs. Thanks to suggestions from Michael and others.

'This code goes into an include file in a custom directory for the customer
DECLARE FUNCTION GET_CHN_PRD(STRING) AS STRING
MACRO CTRU_PATH(prm1)
  IF NOT FNSP(CUST_DIR$) THEN
    DLLPATH$ = "J:\PBSRC\TNET\" + CUST_DIR$ + "\"
  ELSE
    DLLPATH$ = ""
  END IF
  DLLNAME$ = prm1
  DLLNAME$ = DLLPATH$ + DLLNAME$
END MACRO
FUNCTION CallDll (szLib AS STRING, szProc AS STRING,Param1 AS STRING, _
 OPT Param2 AS STRING,OPT Param3 AS STRING,OPT Param4 AS STRING,OPT Param5 AS STRING) AS STRING
  hLib??? = LoadLibrary(BYCOPY szLib)
  IF hLib??? THEN
    dwProc??? = getProcAddress (hLib???,BYCOPY szProc)
    SELECT CASE szProc
      CASE "GET_CHN_PRD"
         CALL DWORD dwProc??? USING GET_CHN_PRD(Param1) TO lRet$
    END SELECT
  ELSE
    MSGBOX "Required DLL " + szLib + " is not present. " ,%MB_OK OR %MB_ICONWARNING,"File not found"
  END IF
  IF hLib??? THEN
    FreeLibrary  hLib???
  END IF
  FUNCTION = lRet$
END FUNCTION


'This code is in PBMAIN' CTRU is true if the correct customer is using the prgm

IF CTRU THEN
   CTRU_PATH("LBCHNPRD.DLL") 'returns local development or customer exe path
   CHN_PRD$ = CALLDLL(DLLNAME$,"GET_CHN_PRD",BYCOPY F1.ACTNR$)
   'Can pass up to 5 parameters see definition above
   ...continues here
END IF