How to export an array from a DLL? - c++

Question

I can`t export an array from a DLL. Here is my code:
" DLL header "
#ifdef EXPORT
#define MYLIB __declspec(dllexport)
#else
#define MYLIB
#endif
extern "C" {
/* Allows to use file both with Visual studio and with Qt*/
#ifdef __cplusplus
MYLIB double MySum(double num1, double num2);
extern MYLIB char ImplicitDLLName[];
#else
extern Q_DECL_IMPORT char ImplicitDLLName[];
Q_DECL_IMPORT double MySum(double num1, double num2);
#endif
}
" DLL source"
#define EXPORT
#include "MySUMoperator.h"
double MySum(double num1, double num2)
{
return num1 + num2;
}
char ImplicitDLLName[] = "MySUMOperator";
" client main.cpp"
int main(int argc, char** argv)
{
printf("%s", ImplicitDLLName);
}
When building I am getting from the linker this error:
Error 2 error LNK2001: unresolved external symbol _ImplicitDLLName \Client\main.obj
// My purpose of exporting the array is to study export of different data structs from DLLs
How to cope with the error raised by linker and what rules are violated?
*UPDATE: *
IDE Visual Studio 2010.
Client - is written on C++, also DLL is on C++

Answer 1

Assuming you're linking your import library correctly (and thats a big assumption), you're not declaring MYLIB correctly for importing symbols:
This:
#ifdef EXPORT
#define MYLIB __declspec(dllexport)
#else
#define MYLIB
#endif
Should be this:
#ifdef EXPORT
#define MYLIB __declspec(dllexport)
#else
#define MYLIB __declspec(dllimport)
#endif
Keep in mind we've little context to work with. It looks like you're trying to consume this from a C-compiled application, but without more info I can't be sure. If that is the case, then Q_DECL_IMPORT had better do the above or it still will not work. I'd start with a basic "C" linkage export and work your way up from there.
Sample EXPORTS.DLL
Exports.h
#ifdef EXPORTS_EXPORTS
#define EXPORTS_API __declspec(dllexport)
#else
#define EXPORTS_API __declspec(dllimport)
#endif
extern "C" EXPORTS_API char szExported[];
Exports.cpp
#include "stdafx.h"
#include "Exports.h"
// This is an example of an exported variable
EXPORTS_API char szExported[] = "Exported from our DLL";
Sample EXPORTSCLIENT.EXE
ExportsClient.cpp
#include "stdafx.h"
#include <iostream>
#include "Exports.h"
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
cout << szExported << endl;
return 0;
}
Output
Exported from our DLL