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- <html>
- <head>
- <title>open</title>
- <body bgcolor=#ffffff>
- <h2 align=center>open</h2>
- <h4 align=center>OS/161 Reference Manual</h4>
- <h3>Name</h3>
- open - open a file
- <h3>Library</h3>
- Standard C Library (libc, -lc)
- <h3>Synopsis</h3>
- #include <unistd.h><br>
- <br>
- int<br>
- open(const char *<em>filename</em>, int <em>flags</em>);<br>
- int<br>
- open(const char *<em>filename</em>, int <em>flags</em>, int <em>mode</em>);<br>
- <h3>Description</h3>
- open opens the file, device, or other kernel object named by the
- pathname <em>filename</em>. The <em>flags</em> argument specifies how
- to open the file. The optional <em>mode</em> argument is only
- meaningful in Unix (or if you choose to implement Unix-style security
- later on) and can be ignored.
- <p>
- The flags argument should consist of one of
- <blockquote><table width=90%>
- <tr><td>O_RDONLY</td> <td>Open for reading only.</td></tr>
- <tr><td>O_WRONLY</td> <td>Open for writing only.</td></tr>
- <tr><td>O_RDWR</td> <td>Open for reading and writing.</td></tr>
- </table></blockquote>
- It may also have any of the following flags OR'd in:
- <blockquote><table width=90%>
- <tr><td>O_CREAT</td> <td>Create the file if it doesn't exist.</td></tr>
- <tr><td>O_EXCL</td> <td>Fail if the file already exists.</td></tr>
- <tr><td>O_TRUNC</td> <td>Truncate the file to length 0 upon open.</td></tr>
- <tr><td>O_APPEND</td> <td>Open the file in append mode.</td></tr>
- </table></blockquote>
- O_EXCL is only meaningful if O_CREAT is also used.
- <p>
- O_APPEND causes all writes to the file to occur at the end of file, no
- matter what gets written to the file by whoever else. (This
- functionality may be optional; consult your course's assignments.)
- <p>
- open returns a file handle suitable for passing to
- <A HREF=read.html>read</A>,
- <A HREF=write.html>write</A>,
- <A HREF=close.html>close</A>,
- etc. This file handle must be greater than or equal to zero. Note
- that file handles 0 (STDIN_FILENO), 1 (STDOUT_FILENO), and 2
- (STDERR_FILENO) are used in special ways and are typically assumed by
- user-level code to always be open.
- <h3>Return Values</h3>
- On success, open returns a nonnegative file handle. On error, -1 is
- returned, and <A HREF=errno.html>errno</A> is set according to the error
- encountered.
- <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>ENODEV</td> <td>The device prefix of <em>filename</em> did
- not exist.</td></tr>
- <tr><td>ENOTDIR</td> <td>A non-final component of <em>filename</em>
- was not a directory.</td></tr>
- <tr><td>ENOENT</td> <td>A non-final component of <em>filename</em>
- did not exist.</td></tr>
- <tr><td>ENOENT</td> <td>The named file does not exist, and O_CREAT
- was not specified.</td></tr>
- <tr><td>EEXIST</td> <td>The named file exists, and O_EXCL was
- specified.</td></tr>
- <tr><td>EISDIR</td> <td>The named object is a directory, and it
- was to be opened for writing.</td></tr>
- <tr><td>EMFILE</td> <td>The process's file table was full, or a
- process-specific limit on open files
- was reached.</td></tr>
- <tr><td>ENFILE</td> <td>The system file table is full, if such a
- thing exists, or a system-wide limit
- on open files was reached.</td></tr>
- <tr><td>ENXIO</td> <td>The named object is a block device with no
- mounted filesystem.</td></tr>
- <tr><td>ENOSPC</td> <td>The file was to be created, and the
- filesystem involved is full.</td></tr>
- <tr><td>EINVAL</td> <td><em>flags</em> contained invalid values.</td></tr>
- <tr><td>EIO</td> <td>A hard I/O error occurred.</td></tr>
- <tr><td>EFAULT</td> <td><em>filename</em> was an invalid pointer.</td></tr>
- </table></blockquote>
- </body>
- </html>
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