Question on Global variables in a DLL

[Mannish Bhandari]

In a DLL, is it true that its global variables are only valid while inside that DLL and not shareable to the Main prog which calls that DLL ?

I would like to ensure that all the Global variables in a DLL can only work inside that DLL, and not seen by the Main calling prog.

[Eric Pearson]

That is correct.

[Mannish Bhandari]

Thanks Eric

[George Bleck]

Via direct source code invocation NO (i.e., without use of pointers or memory peeking). But most definitely YES if you pass pointers.

For example, given...

DLL

GLOBAL gstrVariable AS STRING

SUB SetGlobal()
   gstrVariable = "Hi I am data"
END SUB

SUB GetPointer(BYREF dwdPassed AS DWORD)
   SetGlobal
   dwdPassed = VARPTR(gstrVariable)
END SUB

MainProgram

SUB PBMAIN()
   LOCAL pstrVariable AS STRING PTR
   GetPointer(pstrVariable)
   ? @pstrVariable
END SUB

NOTE: Yes I know horrible example

If you pass the pointer value outside the DLL to the calling EXE it can most definitely access the value of your global.

[Eric Pearson]

I think you need an EXPORT in there somewhere. But in this case, the OP is trying to avoid sharing the values between modules. Yes there are workarounds if you want to purposely bypass the default behavior.

[George Bleck]

Yeah yeah the export as I said bad example. It was more to set the tone it CAN be done. Can also peek account the DLL memory space as it is withing your own. Depends on how bad that global needs to be "protected".

[Stuart McLachlan]

It was more to set the tone it CAN be done. Can also peek account the DLL memory space as it is withing your own. Depends on how bad that global needs to be "protected".

Given the OP's
"would like to ensure that all the Global variables in a DLL can only work inside that DLL, and not seen by the Main calling prog."
your posts are a bit like:
"Can I see a black cat in a dark cellar at night? Yes. If it shiines its flashlight on itself"

(Note the word "flashlight" used to avoid disturbing people in the US. I would normally have said torch" )

[Mannish Bhandari]

What is OP?

[Stuart McLachlan]

What is OP?

Depending on context: "Original Post" or "Original Poster" i.e. normally post #1 in the thread but also maybe something subsequently posted by the original poster.

[Dale Yarker]

(Note the word "flashlight" used to avoid disturbing people in the US. I would normally have said torch" )

Can I make that:
"(Note the word "flashlight" used to avoid disturbing certain people in the US. I would normally have said torch" ) ?

((and some how I suspect that won't happen again for a while [end ] ))

[Christopher Becker]

Eric, I'm not OP, but it's an interesting question and I hadn't ever considered the answer. Thanks for answering. Follow-on question, what about pointers? Could a pointer inside the MAIN be passed to a DLL and the reference remain faithful?

I guess I could code it myself to test. But I'm lazy at the moment. But if it works, and you needed global variables in a DLL, I suppose a work-around would be to make them available via pointers. I still wish there was a way to refer to an array with a pointer in PB.

[Dale Yarker]

See post 4.
Will also work with GLOBAL in dot exe and pointer in DLL.
Use a "helper" function in DLL to exchange pointer. (as in post 4)
Will remain "faithful" (valid) unless DLL is unloaded. (re-exchange pointer if DLL reloaded)

I still wish there was a way to refer to an array with a pointer in PB.

How about pointer to first array element, pass pointer, then DIM AT in other module? ("Helper" function would also pass/receive LBOUND and UBOUND.)

Cheers,

[Stuart McLachlan]

I still wish there was a way to refer to an array with a pointer in PB.

WHat do you mean by "refer to an array" ?

Have you read Help on "Pointers To Arrays"?
Also Help on "Varptr" and "Passing Arrays"

[Stuart McLachlan]

E But if it works, and you needed global variables in a DLL, I suppose a work-around would be to make them available via pointers.

or, as Bob wrote in Help:

GLOBAL variables are not shared between programs and DLLs or between multiple instances of the same DLL. That is, a GLOBAL variable is only global within its own module. The simplest way to expose a variable to a DLL is to pass the variable (by reference) to the target DLL

[Mike Doty]

A passed array can be copied into a global array and the original array can be shared with with PbMain.
Next post passes an array from PbMain using join binary into a global array in a DLL function.

[Mike Doty]

PassArray JOIN$(sArray(), BINARY), LBOUND(sArray), UBOUND(sArray)

#COMPILE EXE
DECLARE SUB PassArray LIB "MyDll.Dll"(s AS STRING,low AS LONG,high AS LONG)
GLOBAL gs() AS STRING   'does not have to be global

FUNCTION PBMAIN
 REDIM gs(1)
 ARRAY ASSIGN gs()="Cool","beans"
 PassArray JOIN$(gs(),BINARY),LBOUND(gs),UBOUND(gs)
END FUNCTION

#COMPILE DLL
GLOBAL gs() AS STRING
DECLARE SUB PassArray LIB "MyDll.Dll"(s AS STRING,low AS LONG, high AS LONG)

SUB PassArray (s AS STRING,low AS LONG,high AS LONG) EXPORT
 REDIM gs(low,high)  'redim to correct number of elements
 PARSE s,gs(),BINARY 'parse into global array
END SUB

[Dale Yarker]

isn't that passing the contents of an array into an identical but totally separate array? Any changes in one will not "appear" in the other.

[Stuart McLachlan]

Pass array to a DLL function that copies array to a global array[code]

Alternatively, see Variant Data Types

[Mike Doty]

> isn't that passing the contents of an array into an identical but totally separate array? Any changes in one will not "appear" in the other.
Dale,
True

Post number 1
In a DLL, is it true that its global variables are only valid while inside that DLL and not shareable to the Main prog which calls that DLL ?

I would like to ensure that all the Global variables in a DLL can only work inside that DLL, and not seen by the Main calling prog.

[Dale Yarker]

Mannish,

Thank you. You may have gotten your answer early, but it still sparked a good discussion.