Load a variable from DLL to .exe

[c0y454]

Hey all,

I've made an experimental .dll (I'm new to dlls) that is supposed to export a variable to the calling .exe

I've tried this(excerpt):
DLL:extern __declspec(dllexport) int mytestvar = 125;
EXE:

#include <windows.h>
#include <conio.h>
#include <iostream>
int _tmain(int argc, _TCHAR* argv[])
{
    HINSTANCE hinstLib; 
    BOOL fFreeResult ;
 
    hinstLib = LoadLibrary(TEXT("MyDll.dll")); 

    if (hinstLib != NULL) 
    { 
  	
     GetProcAddress(hinstLib, "mytestvar");
     extern __declspec(dllimport) int* mytestvar;
     std::cout << mytestvar << std::endl;
 
     fFreeResult = FreeLibrary(hinstLib); 
    } 
	_getch();
	return 0;
}

This results in a linker error (2001, 1120).
I'm not sure how to do this, and MSDN only provides sparse examples.

Could someone help me with this, please?

Thanks in advance!

[kbw]

You need to show the full error text as generated by the linker.

[c0y454]

3>MyDLL.obj : error LNK2001: unresolved external symbol "__declspec(dllimport) int * mytestvar" (__imp_?mytestvar@@3PAHA)
3>F:\C++\Dll exp\Release\MyDLL.exe : fatal error LNK1120: 1 unresolved externals

Thats what I get.

[kbw]

That's a bit of a mess. Forget exporting data for a start.

I'll assume you're using a Microsoft C compiler. The export/import syntax varies across compilers. If you don't have one, you can download an Express Edition of something.

In the TEST.DLL, create a function in a .c file (not .cpp) like:

__declspec(dllimport) const char* GetText(void)
{
    return "hello world";
}

In the EXE your code should look something like:

#include <windows.h>
#include <stdio.h>

typedef const char* GetTextFunc(void);

int main()
{
    HINSTANCE h = LoadLibrary("TEST.DLL");
    if (h)
    {
        GetTextFunc* GetText = GetProcAddress(h, "GetText");
        if (GetText)
        {
            printf("%s\n", GetText());
        }
        FreeLibrary(h);
    }

    return 0;
}

I just typed this into the browser, so you'll have to fix any syntax errors.

[c0y454]

First of all, thanks kbw!!

You are quite right, I am using Visual Studio 2010 Professional, Dreamspark edition.

I managed to compile the code, first as c then also as c++ by exporting the c interface (from msdn).
NOTE: It is "__declspec(dllexport)" and not dllimport!!

This is the final working c++ version:

DLL:

#ifdef __cplusplus
extern "C" {
#endif

__declspec(dllexport) const char* GetText(void)
{
    return "Hello World!";
}

#ifdef __cplusplus
}
#endif 

EXE:

#include <windows.h>
#include <stdio.h>
#include <conio.h>

typedef const char* GetTextFunc(void);

int _tmain(int argc, _TCHAR* argv[])
{
    HINSTANCE h = LoadLibrary(TEXT("DLLx1.DLL"));
    if (h)
    {
        GetTextFunc* GetText = (GetTextFunc*)GetProcAddress(h, "GetText");
        if (GetText)
        {
            printf("%s\n", GetText());
        }
        FreeLibrary(h);
    }

	_getch();
    return 0;

}