The io module contains basic input and output routines.

A quick summary:

Reader and Writer traits

These traits define the minimal set of methods that anything that can do input and output should implement.

ReaderUtil and WriterUtil traits

Richer methods that allow you to do more. Reader only lets you read a certain number of bytes into a buffer, while ReaderUtil allows you to read a whole line, for example.

Generally, these richer methods are probably the ones you want to actually use in day-to-day Rust.

Furthermore, because there is an implementation of ReaderUtil for <T: Reader>, when your input or output code implements Reader, you get all of these methods for free.

print and println

These very useful functions are defined here. You generally don't need to import them, though, as the prelude already does.

stdin, stdout, and stderr

These functions return references to the classic three file descriptors. They implement Reader and Writer, where appropriate.