How to import DLL function from a separate C file

Hi there,

I am trying to create a function in a separate .C file (not the main.c) that imports the DLL functions. Below is what I have, but it doesn't compile.

//importDLL.c

Code:

#include "importDLL.h"
#include <windows.h>

void importDLL()
{
    typedef int (*importFunction)();
    importFunction impFcn;
    HINSTANCE hinstLib = LoadLibrary("someDLL.dll");
    impFcn = (importFunction)GetProcAddress(hinstLib, "impFcn");
}

//importDLL.h

Code:

void importDLL(void);

The problem is in main.c it doesn't recognize the imported DLL function "impFcn". How can I fix it?

Wait. Is this C, or C++? Also, what does "does not compile" mean? What are the errors?

Originally Posted by Elysia

Wait. Is this C, or C++? Also, what does "does not compile" mean? What are the errors?

It's for both C and C++. When it compiles, the main function doesn't recognize the imported DLL function.

Does it compile or doesn't it?

There must be a function with the non-mangled name impFcn in the dll you are loading or GetProcAddress() will return null. You have not given us any of the DLL code so there is no way we can tell you what is wrong.

Originally Posted by high123_98

It's for both C and C++. When it compiles, the main function doesn't recognize the imported DLL function.

Declare all of your DLL imports as "extern C". C++ functions are by default subject to name-mangling (which necessarily precludes class members from being used as such entry points, of course). Also, be explicit about your calling convention (lest you break your ABI elsewhere, too)...

You variable impFcn is local to your function. You need to be able to access it from main, so it needs to be global or better yet the return value of your import function.

You variable impFcn is local to your function.

Wow I cannot believe I did not see that but you are absolutely right. impFcn will go out of scope at the end of the function. Most of use were concentrating on what the function was doing instead of seeing the obvious problem of scope. Nice catch.