What is dllspec(dllimport) and dllspec(dllexport) means

Question

After googling, i came to know that Dllimport makes the function available for other modules,

is it mandatory to declare function with extern \"c\" identifier?

A

Answer 1

__declspec(dllexport) exports a symbol. It makes it available from outside a DLL.

__declspec(dllimport) imports a symbol. It practically says "this symbol is not defined in this application, it needs to be imported from a DLL file".

You don't have to declare it with extern "C". If you don't use extern "C", then the symbol will be exported as a C++ symbol, and you will only be able to call it from C++ (and languages that support calling C++ DLLs). If you use extern "C", then the symbol will be exported as a C symbol, and you will be able to call it from languages that support caling C DLLs.

If you want to use your DLL in C#, you will need to use extern "C".

Here is an excellent tutorial that shows you how to use a C++ DLL in C#: How to marshal a C++ class. I have used solution A in many projects at work.

Also, here is a short tutorial on how you can use a C++ DLL in another C++ application: How to create and use DLL in C++.