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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 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 ‘<samp><span class="samp">b</span></samp>’ 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 “an ordinary file of text” 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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