7.1 What are library interfaces?

Interfaces for libraries may be any of the following (and more):

• global variables: both names and types
• global functions: argument types and number, return types, and function names
• standard input, standard output, standard error, and file formats
• sockets, pipes, and other inter-process communication protocol formats

Note that static functions do not count as interfaces, because they are not directly available to the user of the library.