Dll not found

[marclurr]

Hello there,

I'm currently playing with creating and using DLLs with MinGW.

I've written the following files:

test.h

#ifndef __TEST_H__
#define __TEST_H__

int addOne(int);

#endif

test.c

#include "test.h"

int addOne(int i)
{
    return i + 1;
}

test_test.c

#include <stdio.h>
#include "test.h"

int main()
{
    int i = addOne(13);
    printf("%d\n", i);
    return 0;
}

I compliled my DLL using the following line:

gcc -Wall -shared test.c test.dll

I then compile the application using this line:

gcc test_test.c test.dll -o test_test.exe

Running the file test_test.exe worked fine. But when I moved test.dll to a folder called lib and recompiled test_test with

gcc test_test.c lib/test.dll -o test_test.exe

trying to run the application results in an error mentioning that test.dll cannot be found. I'm unable to find any decent information on this so if someone could explain to me why this is and what can be done to allow test_test.exe to look in the correct place for test.dll I would be very greatful.

Thanks
marclurr

[tabstop]

As a silly test, what about

gcc test_test.c lib\test.dll -o test_test.exe

I'm assuming that the lib folder is in the current folder you're typing the command from.

[marclurr]

Hello thanks for the quick reply,

Yes your assumption is correct. i.e. the directory structure looks like the following:

[edit]root\test_test.c[/edit]
root\test_test.exe
root\lib\test.dll

I tried replacing / with \ but it made no difference. I should note that it compiles fine either way.

[tabstop]

Yeah I missed that it was compiling fine and blowing up at runtime. I'm guessing then that there's a path issue. Perhaps reading Search Path Used by Windows to Locate a DLL may help.

[DeadPlanet]

I'm surprised that your DLL compiles at all. I always thought that DLLs had to contain the DLLMain Function, but I guess not. Anyway, to export your addOne function you should add __declspec(dllexport) before the function definition (so it should now look like '__declspec(dllexport) int addOne(int i)').

Usually when you compile a DLL with MinGW it will give you a .a file along with the DLL, this is the file you should link with. If your dll is called test then the library file should be called libtest.a.

The DLL only needs to be in the same directory (or the system directory) as the executable when run, it does not need to be used for compiling against.

[marclurr]

Thanks for the replies. The msdn page gad some useful information.

Regarding DeadPlanets reply, how do you compile to get the .a and the .dll output? As with the commands outlined above I only got the .dll.

Cheers

[DeadPlanet]

Looking around, it looks as if you can just link straight against the DLL with MinGW. It seems like you can use a library file, but it isn't necessary. I'm really not sure anymore.

Sorry if anything I said was misleading.

(All DLLs I have written and seen use __declspec(dllexport) before function definitions so that should be right, but maybe it also isn't necessary.)

[tabstop]

I believe DeadPlanet's point was that, by default, if you ask for a library gcc will give you a file with a .a extension (since that's the "standard" on *nix systems). Since you specified the .dll extension, gcc was more than happy to call it that instead.

Also, since you "linked" with the library itself, that is probably why you didn't need the export manifest.

If you had wanted something that also needed to work with Visual Studio, I'm not sure how much of this you could still get away with (since that's a different linker).

[marclurr]

Ahh thanks for the info. I don't usually develop on Windows, but since I'm home over Easter that's all there is. It's useful stuff to know so thanks