whats the different betwwen the lib and DLL?

[Chris]

I 've a simple question here.
Can someone explain to me whats the different between the lib and DLL?

If I plan to write a Serial Port driver and I require to do the following things...

• A function to open the serial port like OpenPort(char *PortNo)
• A Send data function like Send2Mobile(char *data)
• A CALLBACK function to the main program when received a data from serial port. This call back function might return the data in structure form.

That the minimum function that I need, hope someone can give me some idea.

So far I can write a DLL after getting the guide line from parksie
but not able to write a call back function.


regards,
Chris.C

[CornedBee]

The difference between a static library (lib) and a dynamic link library (dll) is that the code from the lib is directly included in your program while the code from the dll is only referenced. A lib is a collection of code, and if the linker detects the usage of this code in your program, it inserts the code into you exe. A dll is also a collection of code, but if the linker detects usage of this code, a reference to the code of the dll is inserted. This means that a dll needs only to be loaded once for all apps that use it, while a lib is included in every app that uses it. The advantage of libs is that you don't need to distribute more than one file (probably).

Callbacks:
Do you mean you want to call a VB function?
A VB callback must be located in the main module. Watch out for ByVal and ByRef parameter passing conventions.
In C, you have to declare a pointer to the callback function, like this:

typedef return type (__stdcall * TYPENAME)(parameter list);

And you have to get the address of the function, for example by an init function:

void __stdcall InitDriver(TYPENAME pfnCallBack);

which saves the address of the function and has to be called from VB like this:

private declare sub InitDriver(ByVal pfn as long)

call InitDriver (addressof Callbackfunc)

You can later call this function from the DLL like this:

pfnCallBack(parameter);

Just don't forget:

int i = 5;
int *pi = &i;
PINT p = &i;

pfnCallBack( i,          // this is a value, use ByVal
                    &i,        // this is a pointer, use ByRef
                    pi,        // also a pointer
                     p);      // also a pointer

Therefor, this is the callback:

public sub CallBack (ByVal i as long, ByRef pi1 as long, ByRef pi2 as long, ByRef pi3 as long)
.
.
.
end sub

[Chris]

Thx cornedBee, finally i manage to work out the CALLBACK but I still can not passing a structure back from DLL to VB/VC external program.

Can you please look into this thread

regards,