Continuing on binary input and output


See the lead-in to this section for a description of the constraints on and effects of the other arguments. If procedure returns, call-with-input-file closes the input port and continuing on binary input and output the values returned by procedure. If textual-input-port reaches end of file before the start of the external representation of a datum is found, the eof object is returned. For textual ports, the representation of a position is unspecified; it may not be an exact nonnegative integer and, even if it is, it may not represent either a byte or character displacement in the underlying stream. A binary port allows a program to read or write 8-bit unsigned bytes, or "octets," from or to the underlying stream.

If procedure returns, a string containing the characters accumulated in the port is created, the accumulated characters are cleared from the port, the port's position is reset to zero, and the string is returned from call-with-string-output-port. Some decoders have less than 2 n output lines; in such cases, at least one output pattern will be repeated for different input values. Digital circuits Continuing on binary input and output logic. The following shows the use of open-input-filereadand close-port in an expression that gathers a list of objects from the file named by "myfile.

These procedures are provided for backward compatibility with the Revised 5 Report; they are not actually more convenient to use than close-port. Please help improve this article by adding citations to reliable sources. Procedures for opening other kinds of ports, e. Closing a port that has already been closed has no effect.

For textual ports, the representation of a position is unspecified; it may not be an exact nonnegative integer and, even if it is, it may not represent either a byte or character displacement in the underlying stream. Electronically reproduced by permission. If new data is written at that position, the contents of each intervening position is unspecified. Otherwise, the next available character is returned and the port's position is advanced one character. For output, any eol style except none causes line-feed characters to be converted into the specific one- or two-character continuing on binary input and output associated with the eol style.

If procedure returns, a string containing the characters accumulated in the port is created, the accumulated characters are cleared from the port, the port's position is reset to zero, and the string is returned from call-with-string-output-port. The behavior of with-output-to-file is unspecified if a continuation created outside of thunk is invoked before thunk returns. In addition to the codec and eol style, a transcoder encapsulates just one other piece of information: If binary-input-port continuing on binary input and output at end of file, the eof object is returned.

These arguments are described below. An example of this is a seven-segment decoderwhich converts an integer into the combination of segment control signals needed to display the integer's value on a seven-segment display digit. Three standard codecs are provided:

If thunk returns, the port is closed and the current output port is restored to its old value. If the byte stream is at end of file, r! For textual ports, the representation of a position is unspecified, as described in the entry continuing on binary input and output port-position above, but pos must be an appropriate position for the textual port, which is usually guaranteed to be the case only if it was obtained from a call to port-position on the same port.

An input port often points to a finite stream, e. An example of this is a seven-segment decoder continuing on binary input and output, which converts an integer into the combination of segment control signals needed to display the integer's value on a seven-segment display digit. There are three standard file options: A transcoder encapsulates a codec that determines how characters are represented as bytes.

If the port is an output port, closing the port explicitly also ensures that buffered data is written to the underlying stream. The error-handling mode is ignoreraiseor replace. Otherwise, the next available byte is returned as an unsigned 8-bit quantity, i.