TextStream & Command Line Interface

Global IO Functions

• print("...") with Newline,
  • calls cout.writeLine().
• readLine() -> String reads up to Newline,
  • calls cin.readLine().
• input("Name? ") -> String
  • as in Python,
  • calls cout.write(), then cin.readLine().
  • input(String prompt = "") -> String

TextStream

For input / output of text.

Writing

• cout.write("...") without newline.
• cout.writeLine("...") with newline.

Reading

• cin.read() -> String reads
  • everything from the istream user-level cache (if not empty),
  • or (otherwise) everything from the kernel buffer/cache:
    • With pipes/sockets this is everything currently in the kernel pipe/socket buffer (typically up to 64 KB). Blocks when this buffer is empty. Only when the pipe/socket is closed (and no data is buffered anymore), then it returns "".
    • With files this is everything currently in the kernel “read ahead” cache (typically 64 to 256 KB). Blocks when this cache is empty. Only when the end of file is reached (and no data is buffered anymore), then it returns "".
• cin.readAll() -> String reads everything until the end of the file.
  • With pipes/sockets, it blocks until the pipe/socket is closed.
• cin.readLine() -> String reads until newline (or end of file).
  • The newline character is removed from the line.
    • \n, \r, \r\n are recognized as (a single) newline.
    • (Maybe even \n\r from AmigaOS, and NEL/U+0085 from EBCDIC/IBM.)
  • With pipes/sockets it blocks until a line is available (or pipe/socket is closed).
  • When the end of file is reached, then it returns "".
  • But as empty lines are also read as "", you need to check atEnd() here.
• cin.readGraphemeCluster() -> String reads a single grapheme cluster (mostly a character).
  • Returns a String, as UTF-8 “characters”/grapheme clusters may consist of multiple code points (therefore called a “grapheme cluster”).
  • With pipes/sockets it blocks until a character is available (or the pipe/socket is closed).
  • When the end of file is reached, then it returns "".
  • Unicode variant of cin.readChar() -> Char.
  • TODO? cin.readCodePoint() -> Char32 reads a single Unicode code point (as Char32).
    • But beware: some grapheme clusters, like emoji, consist of multiple code points.
    • When the end of file is reached, then it returns -1.
• cin.tryToRead() -> String reads everything that is immediately available,
  • possibly/often returns "", it never blocks.
  • Reads everything from the istream user-level cache (if not empty),
  • or (otherwise) everything from the kernel buffer/cache:
    • With pipes/sockets this is everything currently in the kernel pipe/socket buffer (typically up to 64 KB). Returns "" when no data is buffered anymore (then maybe the pipe/socket is closed).
    • With files this is everything currently in the kernel “read ahead” cache (typically 64 to 256 KB). Returns "" when no data is buffered anymore (then maybe the end of file is reached).
  • Meant for polling / busy loops only, so rarely appropriate.
  • You need to check atEnd() separately!
    • As you cannot distinguish “no data available” from EOF or pipe/socket closed.
• cin.atEnd() (instead of cin.isEof())
  • returns True if
    • the end of the file is reached (or the pipe/socket is closed),
    • and no data is buffered anymore (neither in the istream user-level cache, nor in the kernel cache/buffer),
  • Typically necessary to call this function when cin.read() or cin.readLine() return "".

Class Hierarchy

• TextStream
  • StringStream