32 lines
1.2 KiB
Racket
32 lines
1.2 KiB
Racket
#lang scribble/doc
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@require[scribble/manual]
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@require[scribble/eval]
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@require["guide-utils.ss"]
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@title[#:tag "ports"]{Input and Output Ports}
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A @defterm{port} encapsulates an I/O stream, normally for just one
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direction. An @defterm{input port} reads from a stream, and an
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@defterm{output port} writes to a string.
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For many procedures that accept a port argument, the argument is
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optional, and it defaults to either the @defterm{current input port}
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or @defterm{current output port}. For @exec{mzscheme}, the current
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ports are initialized to the process's stdin and stdout. The
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@scheme[current-input-port] and @scheme[current-output-port]
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procedures, whien called with no arguments, return the current output
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and input port, respectively.
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@examples[
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(display "hello world\n")
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(display "hello world\n" (current-output-port))
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]
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Ports are created by various procedures that specific to the different
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kinds of streams. For example, @scheme[open-input-file] creates an
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input port for reading from a file. Procedures like
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@scheme[with-input-from-file] both create a port and install it as the
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current port while calling a given body procedure.
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See @secref["io"] for information about using ports.
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