>     I read from the official document that the .a files in
> mingw-runtime lib directory are import library. But are they binary
> archive files? And if they are import libraries, do they import the
> Win32 API from windows DLL files? And how does this work with gcc?
> Thanks in advance!

What do you mean by "are they binary archive files"?  Yes, they are
binary files, yes they are 'ar' style archives, but no they don't
contain any code like a traditional 'ar' static archive.  An import
library is an aide for linking against the DLL of the same name.  They
work with gcc in that you specify just -lfoo, where foo is the name of
the library, e.g. "-lws2_32".

Thank you for your fast reply, Brian!
So, they are import libraries but where are the corresponding DLLs? Thanks !