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1. Load DLL Failed?

#2707

Posted by: mooncake 2003-10-07 19:56:50

Hi, i try this method, but prompt me error message.. :(

#include "wx/dynlib.h"
...

wxDllLoader *mydll = LoadLibrary("mylib.dll");

163 C:main.cpp cannot convert `HINSTANCE__*' to `wxDllLoader*' in initialization

163 C:main.cpp [Warning] unused variable `wxDllLoader*mydll'

what is the different between wxDllLoader and wxDynamicLibrary?

Thank you.

Meow~

2. Re: Load DLL Failed?

#2708

Posted by: 2003-10-07 20:54:43

I think you're asking a win32 function to return a wxWindows type, try

wxDllType *mydll = wxDllLoader::LoadLibrary("mylib");

wxDllLoader is provided for using static methods, whereas wxDynamicLibrary is a wrapper around it so you may derive your own classes.

3. Re: Load DLL Failed?

#2711

Posted by: mooncake 2003-10-08 07:47:32

Hi Adam, still prompt me error message.. :(

cannot convert `HINSTANCE__*' to `HINSTANCE__**' in

[Warning] unused variable `HINSTANCE__**mydll'

Thank you

Meow~

4. Re: Load DLL Failed?

#2712

Posted by: 2003-10-08 08:11:07

Sorry I left an * in there when I copied your code, it should have been:

wxDllType mydll = wxDllLoader::LoadLibrary("mylib");

5. Re: Load DLL Failed?

#2715

Posted by: mooncake 2003-10-08 18:37:08

Hi Adam,

still prompt me error message.. :(

[Warning] unused variable `HINSTANCE__*mydll'

Meow~

6. Re: Load DLL Failed?

#2717

Posted by: 2003-10-08 21:35:05

It's moaning becase you havn't used the handle you created, you have to do something with it, e.g. Get a system beep on Win32:

   wxDllType mydll = wxDllLoader::LoadLibrary("user32");

   typedef bool (*winbeeptype)(unsigned int);    
   winbeeptype win32_beep = (winbeeptype) wxDllLoader::GetSymbol(mydll, "MessageBeep");
   win32_beep(0xFFFFFFFF);

7. Re: Load DLL Failed?

#2718

Posted by: mooncake 2003-10-08 22:13:55

Hi Adam,

why we need to do like this? Would you mind explain/describe for me about these following codes?

typedef bool (*winbeeptype)(unsigned int);

winbeeptype win32_beep = (winbeeptype) wxDllLoader::GetSymbol(mydll, "MessageBeep");

Thank you.

Meow~

8. Re: Load DLL Failed?

#2720

Posted by: 2003-10-09 17:20:51

Sure, I can try, although all this pointer nonsense is still a bit alien to me.

typedef bool (*winbeeptype)(unsigned int);

is like the prototype of the function, so winbeeptype is type with 1 argument (an unsigned int) and a return type of bool, the same as MessageBeep from the DLL. win32_beep is created from this type:

winbeeptype win32_beep;

Finally the function pointer is asked for providing DLL handle and function name and squeezed into the winbeeptype prototype and it is assigned to win32_beep.

win32_beep = (winbeeptype) wxDllLoader::GetSymbol(mydll, "MessageBeep");

9. Re: Load DLL Failed?

#2722

Posted by: mooncake 2003-10-09 19:14:28

Hi,
    Need time to be understand.. >_<
    How do we know winbeeptype win32_beep ?
    Thank you.

Meow~

10. Re: Load DLL Failed?

#2723

Posted by: 2003-10-09 20:44:19

I'm not sure I know which bit, you don't get, I'll write another example:

// Load library, will attempt to load libname.dll or libname.so in platforms normal way
       wxDllType mydll = wxDllLoader::LoadLibrary("libname");

// Define a type which is capable of holding function pointers to function taking 2 ints and returning one.
       typedef int (*int_func_int_int)(int, int);

// We know funk is like this, 
//
//      int funk(int x, int y)
//      { 
//           int z = (x+y);
//           return (z);
//       }
//
// so a pointer is created ready to hold it
       int_func_int_int p_funk;

// Then the pointer is filled with the reference to funk
       p_funk = (int_func_int_int) wxDllLoader::GetSymbol(mydll, "funk");

// Use p_funk as if it were funk
       int result = p_funk(5,8);

11. Re: Load DLL Failed?

#2752

Posted by: mooncake 2003-10-17 22:02:09

Hi Adam,

I am just back from outstation. So, how do we know the type of function from the dll for wx?

Thanks.

Meow~

12. Re: Load DLL Failed?

#2754

Posted by: 2003-10-17 23:13:09

Well in the first example I looked it up in the win32 docs, for the second I'm assuming we would know, because we had written it. Are you trying to use functions from a 3rd party DLL which you have no import docs or source?

13. Re: Load DLL Failed?

#2755

Posted by: mooncake 2003-10-18 22:16:54

Hi,
Hmm... Not really. Becuase, sometime i will download others dll from the internet, so that we do not know the type or function names...

Meow~

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