Question

I am trying to understand an open source project, where I came across the following class declaration:

class STATE_API AttributeSubject : public AttributeGroup, public Subject
{
public:
    AttributeSubject(const char *);
    virtual ~AttributeSubject();
    virtual void SelectAll() = 0;
    virtual const std::string TypeName() const; 
    virtual void Notify();
    virtual AttributeSubject *CreateCompatible(const std::string &) const;
    virtual AttributeSubject *NewInstance(bool copy) const { return 0; };

    virtual bool VarChangeRequiresReset(void) { return false; };
};

What does STATE_API before the class name AttributeSubject signify? Is it some sort of macro?

Answer 1

It’s probably a typedef to __declspec(dllimport) or __declspec(dllexport) and is used inside DLLs on windows platform to export classes.

Neil is right, it’s a macro.

It usually looks like this:

#ifdef INDSIDE_DLL
    #define STATE_API __declspec(dllexport)
#else
    #define STATE_API __declsped(dllimport)
#endif

You define INSIDE_DLL only in your dll and export all the classes declared with STATE_API macro.