Go to the previous, next section.
This section describes the standard operations on output ports. Following that, some useful custom operations are described.
operation+: output port write-char output-port char
Writes char to output-port and returns an unspecified value.
operation+: output port write-substring output-port string start end
Writes the substring specified by string, start, and end to output-port and returns an unspecified value. Equivalent to writing the characters of the substring, one by one, to output-port, but is often implemented more efficiently.
operation+: output port write-string output-port string
Writes string to output-port and returns an unspecified value.
operation+: output port flush-output output-port
If output-port is buffered, this causes its buffer to be written out. Otherwise it has no effect. Returns an unspecified value.
operation+: output port discretionary-flush-output output-port
If output-port is buffered, this causes its buffer to be written out. Otherwise it has no effect. Returns an unspecified value.
This operation, if defined, is normally identical to
flush-output. However, it is not normally defined, and even when
it is, it is invoked at different times (see section Output Procedures).
procedure+: output-port/operation/write-char output-port
procedure+: output-port/operation/write-substring output-port
procedure+: output-port/operation/write-string output-port
procedure+: output-port/operation/flush-output output-port
procedure+: output-port/operation/discretionary-flush-output output-port
Each of these procedures returns the procedure that implements the
respective operation for output-port. Each is equivalent to, but
faster than, output-port/operation on the respective operation
name:
(output-port/operation/write-char output-port) (output-port/operation output-port 'write-char)
procedure+: output-port/write-char output-port char
procedure+: output-port/write-substring output-port string start end
procedure+: output-port/write-string output-port string
procedure+: output-port/flush-output output-port
procedure+: output-port/discretionary-flush-output output-port
Each of these procedures invokes the respective operation on output-port. For example, the following are equivalent:
(output-port/write-char output-port char) ((output-port/operation/write-char output-port) output-port char)
The following custom operations are generally useful.
operation+: output port buffered-output-chars output-port
Returns the number of unwritten characters that are stored in output-port's buffer. This will always be less than or equal to the buffer's size.
operation+: output port output-buffer-size output-port
Returns the maximum number of characters that output-port's buffer can hold.
operation+: output port set-output-buffer-size output-port size
Resizes output-port's buffer so that it can hold at most size characters. Characters in the buffer are discarded. Size must be an exact non-negative integer.
operation+: output port x-size output-port
Returns an exact positive integer that is the width of output-port
in characters. If output-port has no natural width, e.g. if it is
a file port, #f is returned.
operation+: output port y-size output-port
Returns an exact positive integer that is the height of
output-port in characters. If output-port has no natural
height, e.g. if it is a file port, #f is returned.
procedure+: output-port/x-size output-port
This procedure invokes the custom operation whose name is the symbol
x-size, if it exists. If the x-size operation is both
defined and returns a value other than #f, that value is returned
as the result of this procedure. Otherwise, output-port/x-size
returns a default value (currently 79).
output-port/x-size is useful for programs that tailor their
output to the width of the display (a fairly common practice). If the
output device is not a display, such programs normally want some
reasonable default width to work with, and this procedure provides
exactly that.
procedure+: output-port/y-size output-port
This procedure invokes the custom operation whose name is the symbol
y-size, if it exists. If the y-size operation is defined,
the value it returns is returned as the result of this procedure;
otherwise, #f is returned.
Go to the previous, next section.