Import libraries provide the linker with information about functions from a .dll that might be used by a program. If you try to compile some code without a suitable import library, you could have a linker error, such as:

Error 42: Symbol Undefined _GetWindowInfo@8

Some import libraries are provided with the Digital Mars C++ compiler, but those .lib files have developed a reputation for being out-of-date.

You might be able to use .lib files from another source, such as: dwt-win-importlibs.zip (for dwt-win, announcement)

Import libraries can be created using .def files.