<!-- Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009, 2013 The President and Fellows of Harvard College. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. 3. Neither the name of the University nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. --> <html> <head> <title>write</title> <body bgcolor=#ffffff> <h2 align=center>write</h2> <h4 align=center>OS/161 Reference Manual</h4> <h3>Name</h3> <p> write - write data to file </p> <h3>Library</h3> <p> Standard C Library (libc, -lc) </p> <h3>Synopsis</h3> <p> <tt>#include <unistd.h></tt><br> <br> <tt>ssize_t</tt><br> <tt>write(int </tt><em>fd</em><tt>, const void *</tt><em>buf</em><tt>, size_t </tt><em>nbytes</em><tt>);</tt> </p> <h3>Description</h3> <p> <tt>write</tt> 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> <p> The current seek position of the file is advanced by the number of bytes written. </p> <p> Each write (or <A HREF=read.html>read</A>) operation is atomic relative to other I/O to the same file. Note that the kernel is not obliged to (and generally cannot) make the write atomic with respect to other threads in the same process accessing the I/O buffer during the write. </p> <h3>Return Values</h3> <p> 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, <tt>write</tt> returns -1 and sets <A HREF=errno.html>errno</A> to a suitable error code for the error condition encountered. </p> <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> <p> The following error codes should be returned under the conditions given. Other error codes may be returned for other cases not mentioned here. <table width=90%> <tr><td width=5% rowspan=4> </td> <td width=10% valign=top>EBADF</td> <td><em>fd</em> is not a valid file descriptor, or was not opened for writing.</td></tr> <tr><td valign=top>EFAULT</td> <td>Part or all of the address space pointed to by <em>buf</em> is invalid.</td></tr> <tr><td valign=top>ENOSPC</td> <td>There is no free space remaining on the filesystem containing the file.</td></tr> <tr><td valign=top>EIO</td> <td>A hardware I/O error occurred writing the data.</td></tr> </table> </p> </body> </html>