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| <h3 class="section">4.54 <code>setbuf</code>—specify full buffering for a file or stream</h3> |
| |
| <p><a name="index-setbuf-263"></a><strong>Synopsis</strong> |
| <pre class="example"> #include <stdio.h> |
| void setbuf(FILE *<var>fp</var>, char *<var>buf</var>); |
| |
| </pre> |
| <p><strong>Description</strong><br> |
| <code>setbuf</code> specifies that output to the file or stream identified by <var>fp</var> |
| should be fully buffered. All output for this file will go to a |
| buffer (of size <code>BUFSIZ</code>, specified in `<code>stdio.h</code>'). Output will |
| be passed on to the host system only when the buffer is full, or when |
| an input operation intervenes. |
| |
| <p>You may, if you wish, supply your own buffer by passing a pointer to |
| it as the argument <var>buf</var>. It must have size <code>BUFSIZ</code>. You can |
| also use <code>NULL</code> as the value of <var>buf</var>, to signal that the |
| <code>setbuf</code> function is to allocate the buffer. |
| |
| <p><br> |
| <strong>Warnings</strong><br> |
| You may only use <code>setbuf</code> before performing any file operation other |
| than opening the file. |
| |
| <p>If you supply a non-null <var>buf</var>, you must ensure that the associated |
| storage continues to be available until you close the stream |
| identified by <var>fp</var>. |
| |
| <p><br> |
| <strong>Returns</strong><br> |
| <code>setbuf</code> does not return a result. |
| |
| <p><br> |
| <strong>Portability</strong><br> |
| Both ANSI C and the System V Interface Definition (Issue 2) require |
| <code>setbuf</code>. However, they differ on the meaning of a <code>NULL</code> buffer |
| pointer: the SVID issue 2 specification says that a <code>NULL</code> buffer |
| pointer requests unbuffered output. For maximum portability, avoid |
| <code>NULL</code> buffer pointers. |
| |
| <p>Supporting OS subroutines required: <code>close</code>, <code>fstat</code>, <code>isatty</code>, |
| <code>lseek</code>, <code>read</code>, <code>sbrk</code>, <code>write</code>. |
| |
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