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- <html>
- <head>
- <title>read</title>
- <body bgcolor=#ffffff>
- <h2 align=center>read</h2>
- <h4 align=center>OS/161 Reference Manual</h4>
- <h3>Name</h3>
- read - read data from file
- <h3>Library</h3>
- Standard C Library (libc, -lc)
- <h3>Synopsis</h3>
- #include <unistd.h><br>
- <br>
- int<br>
- read(int <em>fd</em>, void *<em>buf</em>, size_t <em>buflen</em>);
- <h3>Description</h3>
- read reads up to <em>buflen</em> bytes from the file specified by
- <em>fd</em>, at the location in the file specified by the current
- seek position of the file, and stores them in the space pointed to
- by <em>buf</em>. The file must be open for reading.
- <p>
- The current seek position of the file is advanced by the number of
- bytes read.
- <p>
- Each read (or <A HREF=write.html>write</A>) operation is atomic
- relative to other I/O to the same file.
- <p>
- <h3>Return Values</h3>
- The count of bytes read is returned. This count should be
- positive. A return value of 0 should be construed as signifying
- end-of-file. On error, read 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 returned. This
- depends on circumstances and does not necessarily signify
- end-of-file.
- <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%> </td><td> </td></tr>
- <tr><td>EBADF</td> <td><em>fd</em> is not a valid file descriptor, or was
- not opened for reading.</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>EIO</td> <td>A hardware I/O error occurred reading the data.</td></tr>
- </table></blockquote>
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