how to export class instance ?

Question

I create a dll project in vs2015, include 2 modules (2 projects)

project 1

in testDLLint.h

ifdef TESTDLLINT_EXPORTS

define TESTDLLINT_API __declspec(dllexport)

else

define TESTDLLINT_API __declspec(dllimport)

endif

class TESTDLLINT_API CtestDLLint {
public:
CtestDLLint(void);
public:
int m;
};
extern __declspec(dllexport) int myInt;
extern __declspec(dllexport) CtestDLLint myInst;

in file1.c

include "testDLLint.h"

__declspec(dllexport) int myInt; = 0;
__declspec(dllexport) CtestDLLint myInst;

TESTDLLINT_API int fntestDLLint(void) {
return 42;
}

CtestDLLint::CtestDLLint() {
return;
}

project 2

file1.c

pragma comment(lib,"../../Debug/testDLLint.lib")

extern __declspec(dllimport) int myInt; // good
extern __declspec(dllexport) CtestDLLint myInst;

int main(){
myInt = 10; // access myInt from module 1 is ok
myInst.m = 10; // wrong
}

my problem is

1. accessing myInt from dll of module 1 is ok
2. acessing class instance myInst from dll of module 1 is not ok

for accessing class's instance from dll, is it possible? if possible, how to do it ?

thanks a lot

Answer 1

@hitbuyi You have totally missed the purpose of the conditional compilation statements

#ifdef TESTDLLINT_EXPORTS  
#define TESTDLLINT_API __declspec(dllexport)  
#else  
#define TESTDLLINT_API __declspec(dllimport)  
#endif  

In your DLL project in which TESTDLLINT_EXPORTS is defined the preprocessor resolves TESTDLLINT_API to __declspec(dllexport).

In other projects that consume the dll and for which TESTDLLINT_EXPORTS is NOT defined the preprocessor resolves TESTDLLINT_API to __declspec(dllimport).

So the header that declares exported classes, functions and variables should use TESTDLLINT_API, instead of __declspec(dllexport).

For example,

class TESTDLLINT_API CtestDLLint {  
public:  
CtestDLLint(void);  
public:  
int m;  
};  
extern TESTDLLINT_API int myInt;  
extern TESTDLLINT_API CtestDLLint myInst;  

So the same header can be used for the DLL project and other projects that consume DLL exports.

Answer 2

Hello,
in file1.c you import myInt but use dllexport with class myInst:

pragma comment(lib,"../../Debug/testDLLint.lib")

extern __declspec(dllimport) int myInt; // good
extern __declspec(dllexport) CtestDLLint myInst;     // <- why dllexport?

int main(){

I think, you must use dllimport with the class instance.

Read this: 399465.aspx

Regards, Guido