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<h3 class="section">12.17 Text and Binary Streams</h3>

<p>The GNU system and other POSIX-compatible operating systems organize all
files as uniform sequences of characters.  However, some other systems
make a distinction between files containing text and files containing
binary data, and the input and output facilities of ISO&nbsp;C<!-- /@w --> provide for
this distinction.  This section tells you how to write programs portable
to such systems.

   <p><a name="index-text-stream-1104"></a><a name="index-binary-stream-1105"></a>When you open a stream, you can specify either a <dfn>text stream</dfn> or a
<dfn>binary stream</dfn>.  You indicate that you want a binary stream by
specifying the &lsquo;<samp><span class="samp">b</span></samp>&rsquo; modifier in the <var>opentype</var> argument to
<code>fopen</code>; see <a href="Opening-Streams.html#Opening-Streams">Opening Streams</a>.  Without this
option, <code>fopen</code> opens the file as a text stream.

   <p>Text and binary streams differ in several ways:

     <ul>
<li>The data read from a text stream is divided into <dfn>lines</dfn> which are
terminated by newline (<code>'\n'</code>) characters, while a binary stream is
simply a long series of characters.  A text stream might on some systems
fail to handle lines more than 254 characters long (including the
terminating newline character). 
<a name="index-lines-_0028in-a-text-file_0029-1106"></a>
<li>On some systems, text files can contain only printing characters,
horizontal tab characters, and newlines, and so text streams may not
support other characters.  However, binary streams can handle any
character value.

     <li>Space characters that are written immediately preceding a newline
character in a text stream may disappear when the file is read in again.

     <li>More generally, there need not be a one-to-one mapping between
characters that are read from or written to a text stream, and the
characters in the actual file. 
</ul>

   <p>Since a binary stream is always more capable and more predictable than a
text stream, you might wonder what purpose text streams serve.  Why not
simply always use binary streams?  The answer is that on these operating
systems, text and binary streams use different file formats, and the
only way to read or write &ldquo;an ordinary file of text&rdquo; that can work
with other text-oriented programs is through a text stream.

   <p>In the GNU library, and on all POSIX systems, there is no difference
between text streams and binary streams.  When you open a stream, you
get the same kind of stream regardless of whether you ask for binary. 
This stream can handle any file content, and has none of the
restrictions that text streams sometimes have.

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