Cannot export functions in a DLL - c++

Question

I have a .lib which has a function that I want to make into a DLL.
In the project properties, I have done 2 things,
1. In the C/C++ -> General -> Additional Directories: added the path for the .h file.
2. In the Linker-> General -> Additional Dependies: added the path for the .lib file
Then I made an .h file
#ifndef _DFUWRAPPER_H_
#define _DFUWRAPPER_H_
#include <windows.h>
#include "DFUEngine.h"
#ifdef __cplusplus
extern "C" {
#endif
__declspec(dllexport) void helloworld(void);
__declspec(dllexport) void InitDLL();
#ifdef __cplusplus
}
#endif
#endif
and made the .cpp file
#include "stdafx.h"
#include "stdio.h"
#include "DFUWrapper.h"
#ifdef _MANAGED
#pragma managed(push, off)
#endif
BOOL APIENTRY DllMain( HMODULE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
return TRUE;
}
#ifdef _MANAGED
#pragma managed(pop)
#endif
void helloworld(void)
{
printf("hello world DFU");
}
DFUEngine* PyDFUEngine()
{
return new DFUEngine();
}
void delDFUEngine(DFUEngine *DFUe)
{
DFUe->~DFUEngine();
}
void PyInitDLL(DFUEngine *DFUe)
{
return DFUe->InitDLL();
}
I made a test with the function helloword. I can see this function in the DLL but not the InitDLL function.
How can I come around this? Please help

Answer 1

Define the following in your DLL header file
#if defined (_MSC_VER)
#if defined (MY_DLL_EXPORTS)
#define MY_EXPORT __declspec(dllexport)
#else
#define MY_EXPORT __declspec(dllimport)
#endif
#else
#define MY_EXPORT
#endif
Declare your function using that macro
#ifdef __cplusplus
extern "C" {
#endif
MY_EXPORT void helloworld(void);
MY_EXPORT void InitDLL();
#ifdef __cplusplus
}
#endif
And in your .cpp
MY_EXPORT void helloworld(void)
{
printf("hello world DFU");
}
MY_EXPORT void InitDLL()
{
/// blahblah
}
Compile your DLL with MY_DLL_EXPORT defintion....
But be sure that it's not define when you want IMPORT ....

Answer 2

I like exporting functions from DLLs using .DEF files.
This has the added benefit of avoiding name mangling: not only the C++ complex mangling, but also the one happening with __stdcall and extern "C" functions (e.g. _myfunc#12).
You may want to simply add a DEF file for your DLL, e.g.:
LIBRARY MYDLL
EXPORTS
InitDLL #1
helloworld #2
... other functions ...