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<head>
<title>write</title>
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<h2 align=center>write</h2>
<h4 align=center>OS/161 Reference Manual</h4>

<h3>Name</h3>
write - write data to file

<h3>Library</h3>
Standard C Library (libc, -lc)

<h3>Synopsis</h3>
#include &lt;unistd.h&gt;<br>
<br>
int<br>
write(int <em>fd</em>, const void *<em>buf</em>, size_t <em>nbytes></em>);

<h3>Description</h3>

write writes up to <em>buflen</em> bytes to the file specified by
<em>fd</em>, at the location in the file specified by the current
seek position of the file, taking the data from the space pointed
to by <em>buf</em>. The file must be open for writing.
<p>

The current seek position of the file is advanced by the number of
bytes written.
<p>

Each write (or <A HREF=read.html>read</A>) operation is atomic
relative to other I/O to the same file.
<p>

<h3>Return Values</h3>

The count of bytes written is returned. This count should be
positive. A return value of 0 means that nothing could be written,
but that no error occurred; this only occurs at end-of-file on
fixed-size objects. On error, write returns -1 and sets 
<A HREF=errno.html>errno</A> to a suitable error code for the error
condition encountered.
<p>

Note that in some cases, particularly on devices, fewer than
<em>buflen</em> (but greater than zero) bytes may be written. This
depends on circumstances and does not necessarily signify
end-of-file. In most cases, one should loop to make sure that all
output has actually been written.
<p>

<h3>Errors</h3>

The following error codes should be returned under the conditions
given. Other error codes may be returned for other errors not
mentioned here.

<blockquote><table width=90%>
<td width=10%>&nbsp;</td><td>&nbsp;</td></tr>
<tr><td>EBADF</td>	<td><em>fd</em> is not a valid file descriptor, or was
			not opened for writing.</td></tr>
<tr><td>EFAULT</td>	<td>Part or all of the address space pointed to by
			<em>buf</em> is invalid.</td></tr>
<tr><td>ENOSPC</td>	<td>There is no free space remaining on the filesystem
			containing the file.</td></tr>
<tr><td>EIO</td>	<td>A hardware I/O error occurred writing 
			the data.</td></tr>
</table></blockquote>

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