What is __declspec and when do I need to use it?

Question

I have seen instances of __declspec in the code that I am reading. What is it? And when would I need to use this construct?

Answer 1

The canonical examples are __declspec(dllimport) and __declspec(dllexport), which instruct the linker to import and export (respectively) a symbol from or to a DLL.

// header
__declspec(dllimport) void foo();


// code - this calls foo() somewhere in a DLL
foo();

(__declspec(..) just wraps up Microsoft's specific stuff - to achieve compatibility, one would usually wrap it away with macros)