How are Header file (.h), Library file (.lib) and DLL (.dll) files related

Question

I have seen in driver libraries these three files. How are the three files related, what is the order in which the files are compiled and what is the content of each file? In addition to this I have also seen .a files are they same as .lib?

Solution

.lib and .dll files are both containers of executables of a Windows library (.o or .obj files), with the former (.lib) containing stuff (functions, definitions, etc) that you have to link statically to the executable file of your project. The latter (.dll) is either already present in your system or you put it into your system, and it is dynamically linked to the executable file of your project.

For Unix/Linux systems, the file-extensions are .a and .so respectively (that is, .a instead of .lib, and .so instead of .dll).

In all cases, when compiling your project you must #include one or more of the .h files provided to you by the library you are using (they are called header files), because that's where the stuff inside the executables of the library get defined.

EDIT

The main advantage of a statically linked library is that it is self-contained (no external dependencies) but it increases the size of your own executable file. The main disadvantage is that future versions must be re-compiled and re-distributed.

For dynamically linked libraries, we re-distribute just the updated library executables. The main disadvantage is that our program relies on the library being already installed on the customer's system.

Comments

[Wakan Tanka]

It should be noted that there is also something which is called "Import Library" check stackoverflow.com/questions/3573475/…