Function pointer returning null

[ambershee]

Hello!

I'm trying to employ DLLs by loading them at run time, but have run into a snag that I have not yet solved.

Essentially, one of my function pointers looks a bit like this (ignoring string type):

string (*GetString)() = 0;

HINSTANCE hinstLib = LoadLibrary("my.dll");

if (hinstLib == NULL)
{
	cout << "Failed to load DLL." << endl;
	return;
}

GetString = (string(__cdecl*)(void))GetProcAddress(hinstLib, "getString");

The code inside the DLL itself looks like this:

#ifndef ASEXPORT
#define DLLIMPORTOREXPORT dllimport
#else
#define DLLIMPORTOREXPORT dllexport
#endif

#ifdef __cplusplus    // If used by C++ code, 
extern "C" {          // we need to export the C interface
#endif

_declspec(DLLIMPORTOREXPORT) string getString() return{"MyString"};

#ifdef __cplusplus    // If used by C++ code, 
}
#endif 

However GetString keeps returning a null pointer. I'm finding this a little hard to debug.

Any suggestions of what to be looking at?

Many thanks for your time,

Luke

[helios]

Windows probably can't find the DLL. Make sure it's either in the working directory or in a directory in the PATH environment variable.

By the way, line 11 of your second snippet shouldn't compile.

[ambershee]

You may well be right, and I'll look into it more- but then it should be finding it without difficulty - because the application actually generates a list of .dll files in the working directory which is where it gets the name of the DLL in LoadLibrary (the code above is a smaller, simplified snippet of a considerably larger application).

I've already rewritten the DLL to look more like this:

Header:

#include <string>

using namespace std;

#ifndef ASEXPORT
#define DLLIMPORTOREXPORT dllimport
#else
#define DLLIMPORTOREXPORT dllexport
#endif

extern "C"_declspec(DLLIMPORTOREXPORT) string getString();

Cpp

#include "stdafx.h"
#include "amplify.h"

#define ASEXPORT


string getString()
{
	return "myString";
}

Thanks again,

Luke

[ambershee]

An update:

It's finding the DLL - but the function pointer is still not working. I really don't know what left to do.