What is it

Preconnected input and output communication channels between a computer program and its environment when it begins execution.

• When a process starts, these handles are automatically opened.

The three IO streams/connections are called:

• stdin, stdout, and stderr

stdin is a stream that handle that your process reads to get information from you.

stdout is a stream that when a process writes conventional output, it is written to this file handle.

stderr is when a process writes diagnostic output to this file handle.

Most programs need to read input, write output, and log errors.

• So stdin, stdout, and stderr are predefined for you, as a programming convenience. This is only a convention, and is not enforced by the operating system.