OK, Im getting a few unresolved externals for some code, and I cant for the life of me figure out why. My googling didnt find anything I could figure out my situation from. Im running VS 2008 on a vista notebook. In a .h there is this: and in the matching .cpp: The two errors Im getting are as follows: 1>SYS_INPUT.obj : error LNK2001: unresolved external symbol "public: __thiscall _input_event::_input_event(void)" (??0_input_event@@QAE@XZ) 1>SYS_INPUT.obj : error LNK2001: unresolved external symbol "public: __thiscall _input_event::~_input_event(void)" (??1_input_event@@QAE@XZ) (naturally and a third telling me there is these 2) I havent used function pointers all that terribly much, but when trying the examples in that "learn c++ in 21 days" they worked fine.

The linker is telling you it cannot find the implementation of struct _input_event's constructor or destructor. Either define them inline in the header, or inside one of your cpp files.

[edit]

Also I thought I'd add some points regarding writing idiomatic C++ code. In C++ we do not typedef structs. This is done in C because subsequent declarations of the struct are required to be prefixed with the struct, keyword and this is considered cumbersome. For example:


struct foo
{
....
};

struct foo myFoo;


However in C++ you can omit the struct keyword in subsequent declarations: foo myFoo;

Lastly in C++ we (generally) prefer to use function objects over function pointers. Additionally the boost library provides boost::bind and boost::function, which provide a fantastic function objects implementation.