CReating a DLL whcih can export 'n' number of functions for a client application

KennedyDayala

Helo All,

I would like to develop a .dll with Qt which can be able to export some 'c' functions to client application. Can experts guide me on this ?

many thanks,

giesbert

you have to sorround the functions with

@
extern "C"
{
// do your functions and export definitions here
}
@

if you use MSVS tool chain. Don't know whether it is also needed for others like gcc etc.

ludde

The easiest way to set up a project for a shared library / DLL is to use the Qt Creator New Project... wizard (and select Other Project / C++ Library). That will give you a good starting point with import / export defines etc.

If you want to make it a pure C DLL, the interface obviously has to be pure C, no C++ classes as return values or parameters.

jim_kaiser

Er.. this ("__declspec(dllexport)" and "__declspec(dllimport)") is required too.. isn't it?

MyDllDef.h
@
#ifdef INMYLIB
#define MYLIBDEF __declspec(dllexport)
#else
#define MYLIBDEF __declspec(dllimport)
#endif
@

MyLib.h
@
#include "MyDllDef.h"

MYLIBDEF void exported_fn();
@

MyApp.cpp
@
#include <MyLib.h>

void runFn()
{
exported_fn();
}
@

You might also need to use the extern C.. Look at this "Stack Overflow":http://stackoverflow.com/questions/2288293/windows-c-extern-declspecdllimport post on it.

ludde

Yeah, that's exactly what you get from the Other Project / C++ Library wizard. That's what I meant by 'import / export defines etc.' (though I agree I could have been a bit more explicit).

jim_kaiser

@ludde: Sorry about that, I hadn't used the feature myself, coding in VS at work.. but you're right the wizard does make it a lot simpler. Cheers :)

[Edit: @gerolf: Thanks for the info.. i noticed the macros in the wizard generated code.. ]

giesbert

But that's only needed on windows for MSVC compiler, mingw does it in another way, so I suggest using Q_DECL_EXPORT / Q_DECL_IMPORT. They map to the correct, compiler specific code.