lang/C/the.ansi.c.programming.language/notes.accompany.ansi.c/sx10a.html

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   9 <title>section 7.1: Standard Input and Output</title>
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  15 <H2>section 7.1: Standard Input and Output</H2>
  16
  17 <p>Note that ``a text stream'' might refer
  18 to input
  19 (to the program)
  20 from the keyboard or output to the screen,
  21 <em>or</em>
  22 input and output from files on disk.
  23 (For that matter,
  24 it can also refer to input and output from other peripheral devices,
  25 or the network.)
  26 </p><p>Note that the stdio library generally does newline translation for you.
  27 If you know that lines are terminated by a linefeed on Unix
  28 and a carriage return on the Macintosh and a
  29 carriage-return/linefeed combination on MS-DOS, you don't have
  30 to worry about these things in C, because the line termination
  31 will always appear to a C program to be a single <TT>'\n'</TT>.
  32 (That is, when reading,
  33 a single <TT>'\n'</TT> represents the end of the line being read,
  34 and when writing,
  35 writing a <TT>'\n'</TT> causes
  36 the underlying system's actual end-of-line representation to be written.)
  37 </p><p>pages 152-153
  38 </p><p>The ``<TT>lower</TT>'' program is an example of a <dfn>filter</dfn>:
  39 it reads its standard input,
  40 ``filters''
  41 (that is, processes)
  42 it in some way, and writes the result to its standard output.
  43 Filters are designed for
  44 (and are only really useful under)
  45 a command-line interface such as the Unix shells
  46 or the
  47 MS-DOS command.com interface.
  48 Obviously, you would rarely invoke a program like <TT>lower</TT>
  49 by itself, because you would have to type the input text at it
  50 and you could only see the output ephemerally on your screen.
  51 To do any real work, you would always redirect the input:
  52 <pre>   lower &lt; inputfile
  53 </pre>and perhaps the output:
  54 <pre>   lower &lt; inputfile &gt; outputfile
  55 </pre>(notice that spaces may precede and follow
  56 the <TT>&lt;</TT> and <TT>&gt;</TT> characters).
  57 Or, a filter program like <TT>lower</TT> might appear in a longer
  58 pipeline:
  59 <pre>   oneprogram | lower | anotherprogram
  60 or
  61         anotherprogram &lt; inputfile | lower | thirdprogram &gt; outputfile
  62 </pre>Filters like these are not terribly useful,
  63 though,
  64 under a Graphical User Interface
  65 such as the Macintosh or Microsoft Windows.
  66 </p><hr>
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  75 This page by <a href="http://www.eskimo.com/~scs/">Steve Summit</a>
  76 // <a href="copyright.html">Copyright</a> 1995, 1996
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