Making Visual C++ DLL from C++ class
- by prosseek
I have the following C++ code to make dll (Visual Studio 2010).
class Shape {
public:
Shape() {
nshapes++;
}
virtual ~Shape() {
nshapes--;
};
double x, y;
void move(double dx, double dy);
virtual double area(void) = 0;
virtual double perimeter(void) = 0;
static int nshapes;
};
class __declspec(dllexport) Circle : public Shape {
private:
double radius;
public:
Circle(double r) : radius(r) { };
virtual double area(void);
virtual double perimeter(void);
};
class __declspec(dllexport) Square : public Shape {
private:
double width;
public:
Square(double w) : width(w) { };
virtual double area(void);
virtual double perimeter(void);
};
I have the __declspec,
class __declspec(dllexport) Circle
I could build a dll with the following command
CL.exe /c example.cxx
link.exe /OUT:"example.dll" /DLL example.obj
When I tried to use the library,
Square* square; square->area()
I got the error messages.
What's wrong or missing?
example_unittest.obj : error LNK2001: unresolved external symbol "public: virtual double __thiscall
...
Square::area(void)" (?area@Square@@UAENXZ)
ADDED
Following wengseng's answer, I modified the header file, and for DLL C++ code, I added
#define XYZLIBRARY_EXPORT
However, I still got errors.
example_unittest.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: __th
iscall Circle::Circle(double)" (__imp_??0Circle@@QAE@N@Z) referenced in function "protected: virtual
void __thiscall TestOne::SetUp(void)" (?SetUp@TestOne@@MAEXXZ)
example_unittest.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: __th
iscall Square::Square(double)" (__imp_??0Square@@QAE@N@Z) referenced in function "protected: virtual
void __thiscall TestOne::SetUp(void)" (?SetUp@TestOne@@MAEXXZ)
example_unittest.obj : error LNK2001: unresolved external symbol "public: virtual double __thiscall
Square::area(void)" (?area@Square@@UAENXZ)
example_unittest.obj : error LNK2001: unresolved external symbol "public: virtual double __thiscall
Square::perimeter(void)" (?perimeter@Square@@UAENXZ)
example_unittest.obj : error LNK2001: unresolved external symbol "public: virtual double __thiscall
Circle::area(void)" (?area@Circle@@UAENXZ)
example_unittest.obj : error LNK2001: unresolved external symbol "public: virtual double __thiscall
Circle::perimeter(void)" (?perimeter@Circle@@UAENXZ)
