Thread: Working with DLL files...

How do I create a dll file, and how can I read from it?


Thank you.

what do you mean by "function address"?
don't i use the functions from the dll like any other function?

yeah i thought about using libs, and i do know how to create one, with borland

but correct me if i'm wrong, the main difference between lib and dll is the fact that i don't link the dll to the exe, unlike with lib, so i always have the exe and dll files. so using a dll file makes it easier for me to up-date my software, i can simply patch the dll file instead the entire exe.

No, even if you use a .lib file, the DLL file is still required. Let's say your dll file has a function that looks like:

Code:

int dllfn(char *cArray);

Without a lib file, you would have to do:

Code:

typedef int (*DLLFN)(char*);
DLLFN dllfn;
char someArray[10];
HMODULE hMod = LoadLibrary("mydll.dll");
dllfn = (DLLFN)GetProcAddress(hMod,"dllfn");
dllfn(someArray);

If you link to the .lib file, then all you would have to do is:

Code:

#include "mydll.h"
...
int i = dllfn(someArray);

In both cases, the dll file is needed and must be included with the .exe file. If you use the .lib file to link, you do not need to include it with the .exe file when you distribute it. The .lib file is only used in the linking process to tell the linker where the dll function are located.

i'm sorry but i don't understand the connection of lib here...
if i could simply put the next code in a function, why would i need to create a lib and link it...

Code:

typedef int (*DLLFN)(char*);
DLLFN dllfn;
char someArray[10];
HMODULE hMod = LoadLibrary("mydll.dll");
dllfn = (DLLFN)GetProcAddress(hMod,"dllfn");

>>i'm sorry but i don't understand the connection of lib here...

The .lib is created automatically when you make the dll. It contains the functions address (location) in the dll (same as GetProcAddress() does). It must be built into the exe (with the header).

Look at 'implicit' (static) v 'explicit' (dynamic) linking.

Sometimes you only need a function occasionally so you link to the dll while the app is running, use the function, free the dll (FreeLibrary() ). As per the code snippet.

Why?

The dll is someone elses work / not included in all versions of the app.

You may not know the name of the dll you want until run time, ie OS or hardware specific.

No changes to the header or .lib are needed if you explicitly link.

Some performance and error issues.