0A library is a package of code that is meant to be reused by many programs.
A static library (also known as an archive) consists of routines that are compiled and linked directly into your program. When you compile a program that uses a static library, all the functionality of the static library becomes part of your executable.
A dynamic library (also called a shared library) consists of routines that are loaded into your application at run time. When you compile a program that uses a dynamic library, the library does not become part of your executable -- it remains as a separate unit. One advantage of dynamic libraries is that many programs can share one copy, which saves space. Perhaps a bigger advantage is that the dynamic library can be upgraded to a newer version without replacing all of the executables that use it.
Because dynamic libraries are not linked into your program, programs using dynamic libraries must explicitly load and interface with the dynamic library. This mechanism can be confusing, and makes interfacing with a dynamic library awkward. To make dynamic libraries easier to use, an import library can be used.
An import library is a library that automates the process of loading and using a dynamic library. On Windows, this is typically done via a small static library (.lib) of the same name as the dynamic library (.dll). The static library is linked into the program at compile time, and then the functionality of the dynamic library can effectively be used as if it were a static library. On Linux, the shared object (.so) file doubles as both a dynamic library and an import library. Most linkers can build an import library for a dynamic library when the dynamic library is created.
