Problems using a DLL

Hello everyone. I´m using Qt 4.2.2 and VisualStudio 2005.
My problem is I wanna make use of a Dll and I only get linking errors related to it.
I want to load the dll at compiling time, so I guess I don´t need to use QLibrary, am I right?
I have a header file with the name of the functions I can call.

Here it is the .h file (loc.h):

Code:

---

#ifndef LOC_H
#define LOC_H
 
#ifdef __cplusplus
extern "C" {
#endif
 
#include <windows.h>
#define LOC_ERR_FRAME_INCOMPL     -1
#define LOC_ERR_LONG              -2
#define LOC_ERR_CRC               -3
 
typedef struct loc_position_t {
  float x;
  float y;
} loc_position_t;
 
 
int loc_getposition(loc_position_t *p);
int loc_ini(void);
int loc_end(void);
 
#ifdef __cplusplus
}
#endif
 
#endif //LOC_H

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I also include the dll file so you can see what it´s wrong.

I have used this code in Code::blocks without a problem, but now I wanna use it with Qt/VisualStudio and I get linking problems everytime I try to compile it.

Can anyone please help me?

Quote:

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Originally Posted by prosass

I have used this code in Code::blocks without a problem, but now I wanna use it with Qt/VisualStudio and I get linking problems everytime I try to compile it.

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There is some __declspec() stuff missing here... :rolleyes: you should create a macro (LOC_EXPORT for instance) which would be defined as Q_DECL_EXPORT when building the library and Q_DECL_IMPORT when linking to it. Then it will be necessary to modify your source :

Code:

---

LOC_EXPORT int loc_getposition(loc_position_t *p);
LOC_EXPORT int loc_ini(void);
LOC_EXPORT int loc_end(void);

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Side note : this is a Window$ specific problem encountered by every newbie that tries to create a .dll under this crappy OS without reading the docs first.:p I say that after personal experience;)

Thanks fullmetalcoder for your answer. The problem is I didn´t create the Dll and I cannot modify it to include the Q_DECL_EXPORT and the Q_DECL_IMPORT. Is there any way I can still use the DLL?

Quote:

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Originally Posted by prosass

Thanks fullmetalcoder for your answer. The problem is I didn´t create the Dll and I cannot modify it to include the Q_DECL_EXPORT and the Q_DECL_IMPORT. Is there any way I can still use the DLL?

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Sounds weird... You mean that you grabbed a dll from some piece of software and want to use it? In this case you will need a SDK (header files and, under Window$, import library) and Qlibrary won't help you if the symbols (functions/classes) you are interested in are not exported using __declspec() (or any equivalent macro)...

I got the DLL from a student at my university who was working on the same piece of hardware and all I got was the file .h with the functions I can use and the Dll itself.
At the moment I don´t think I´m using QLibrary. In the .cpp file I just try to access the functions by calling them:

Code:

---

int err = 0;
        err = loc_ini();
 
        while (1) {
             //Sleep(1);
             err = loc_getposition(&loc_pos);
             //Sleep(500);
             cout << "Posicion x:" << loc_pos.x << endl;
             cout << "posicion y:" << loc_pos.y << endl << endl;
        }
}

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This was enough in Code::blocks but it doesn´t work in QT/VisualStudio. Should I use something like:

Code:

---

QLibrary Sniffer("Sniffer");
 
typedef void (*MyPrototype)();
 MyPrototype myFunction = (MyPrototype) myLib.resolve("mysymbol");
 if (myFunction)
     myFunction();

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Should I use something like that?

Quote:

---

Originally Posted by prosass

I got the DLL from a student at my university who was working on the same piece of hardware and all I got was the file .h with the functions I can use and the Dll itself. This was enough in Code::blocks but it doesn´t work in QT/VisualStudio.

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Which files exactly do you received??? I'm particularly interested in extension like .a or .lib
AFAIK if the compile-time linking doesn't work there are not much chances for it to work at run-time but I might be proved wrong here...

I got the loc.h file that I wrote down in the beggining, the sniffer.dll and the following main.cpp:

Code:

---

#include "loc.h"
#include <windows.h>
#include "iostream.h"
 
loc_position_t loc_pos;
 
int main(void) {
 
        int err = 0;
        err = loc_ini();
 
        while (1) {
             //Sleep(1);
             err = loc_getposition(&loc_pos);
             //Sleep(500);
             cout << "Posicion x:" << loc_pos.x << endl;
             cout << "posicion y:" << loc_pos.y << endl << endl;
        }
}

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That is all I got, do I also need a .lib file to make it work?

Quote:

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Originally Posted by prosass

I got the loc.h file that I wrote down in the beggining, the sniffer.dll and the following main.cpp:
That is all I got, do I also need a .lib file to make it work?

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Well, AFAIK window always require an import library to achieve linking against a dll. The file extension of these libs is .lib for MSVC and .a for gcc/mingw. If your friend did not give you such a lib you should ask for one or for the full sources...