Stdout

Stdout, short for standard output, is one of the standard data streams that a process can use to communicate output to its environment. In POSIX and similar systems, the three standard streams—stdin (input), stdout (output), and stderr (error)—are connected to the process via file descriptors, with stdout typically assigned to file descriptor 1. When a program writes to stdout, its output is intended for the main output channel of the program.

By default, stdout is connected to the terminal that started the process. However, it can be redirected to a file, another device, or a pipeline through shell redirection (for example, using > to write to a file or | to pipe output to another program). Output may be buffered by the runtime or language runtime, which affects when data actually appears.

In C, the standard library exposes stdout as a FILE* stream, used by functions like printf and putchar. In higher-level languages, stdout is often provided as a standard output stream; for example, Python's print writes to sys.stdout, and Java's System.out is a PrintStream bound to stdout. In shells, commands produce output on stdout by default, and redirection or piping can alter where that data goes.

Stdout is distinct from standard error, which uses file descriptor 2 and is intended for diagnostic messages. Redirecting stdout does not affect stderr and vice versa unless explicitly combined.

On Windows, stdout is similarly mapped to the console or a file, and can be redirected; some environments treat text mode conversions differently.