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POMaking Visual C++ DLL from C++ class
 

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  1. POMaking Visual C++ DLL from C++ class
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    <p>I have the following C++ code to make dll (Visual Studio 2010).</p> <pre><code>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); }; </code></pre> <p>I have the __declspec, </p> <pre><code>class __declspec(dllexport) Circle </code></pre> <p>I could build a dll with the following command</p> <pre><code>CL.exe /c example.cxx link.exe /OUT:"example.dll" /DLL example.obj </code></pre> <p>When I tried to use the library, </p> <pre><code>Square* square; square-&gt;area() </code></pre> <p>I got the error messages. What's wrong or missing?</p> <pre> example_unittest.obj : error LNK2001: unresolved external symbol "public: virtual double __thiscall ... Square::area(void)" (?area@Square@@UAENXZ) </pre> <h2>ADDED</h2> <p>Following wengseng's answer, I modified the header file, and for DLL C++ code, I added </p> <pre><code>#define XYZLIBRARY_EXPORT </code></pre> <p>However, I still got errors.</p> <h2>SOLVED</h2> <p>For main program that links example.dll, I didn't link example.lib.</p> <pre><code>cl /MD /EHsc gtest_main.cc example_unittest.cc /I"./include" /link /libpath:"./lib" /libpath:"." gtest_md.lib example.lib /out:gtest_md_release.exe </code></pre> <p>With the addition, everything works fine.</p>
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    1. COI thought DLLs had to use C calling conventions, meaning no C++ member functions. That's just off the top of my head, though.
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    2. COHow did you import the class Circle at CL.exe?
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    3. COYou can export C++ classes in DLL interfaces. The problem is that C++ name mangling is applied to exported symbols. Since there is no standard for name mangling, every compiler does it differently. Sometimes different versions of the same compiler will do it differently. This is usually a bad idea.
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