resource for developing dynamic library

[Bezi]

I need help with how to write a dynamic library in C++,
__declspec(dllexport) kind of stuff.

Can anyone introduce me a good resource, preferably online?

[helios]

http://www.google.com/search?q=how+to+write+a+dll
For UNIX systems it's more or less the same thing save for a few details.