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| <h4 class="subsection">14.9.9 File Times</h4> |
| |
| <p><a name="index-file-access-time-1581"></a><a name="index-file-modification-time-1582"></a><a name="index-file-attribute-modification-time-1583"></a>Each file has three time stamps associated with it: its access time, |
| its modification time, and its attribute modification time. These |
| correspond to the <code>st_atime</code>, <code>st_mtime</code>, and <code>st_ctime</code> |
| members of the <code>stat</code> structure; see <a href="File-Attributes.html#File-Attributes">File Attributes</a>. |
| |
| <p>All of these times are represented in calendar time format, as |
| <code>time_t</code> objects. This data type is defined in <samp><span class="file">time.h</span></samp>. |
| For more information about representation and manipulation of time |
| values, see <a href="Calendar-Time.html#Calendar-Time">Calendar Time</a>. |
| <a name="index-time_002eh-1584"></a> |
| Reading from a file updates its access time attribute, and writing |
| updates its modification time. When a file is created, all three |
| time stamps for that file are set to the current time. In addition, the |
| attribute change time and modification time fields of the directory that |
| contains the new entry are updated. |
| |
| <p>Adding a new name for a file with the <code>link</code> function updates the |
| attribute change time field of the file being linked, and both the |
| attribute change time and modification time fields of the directory |
| containing the new name. These same fields are affected if a file name |
| is deleted with <code>unlink</code>, <code>remove</code> or <code>rmdir</code>. Renaming |
| a file with <code>rename</code> affects only the attribute change time and |
| modification time fields of the two parent directories involved, and not |
| the times for the file being renamed. |
| |
| <p>Changing the attributes of a file (for example, with <code>chmod</code>) |
| updates its attribute change time field. |
| |
| <p>You can also change some of the time stamps of a file explicitly using |
| the <code>utime</code> function—all except the attribute change time. You |
| need to include the header file <samp><span class="file">utime.h</span></samp> to use this facility. |
| <a name="index-utime_002eh-1585"></a> |
| <!-- time.h --> |
| <!-- POSIX.1 --> |
| |
| <div class="defun"> |
| — Data Type: <b>struct utimbuf</b><var><a name="index-struct-utimbuf-1586"></a></var><br> |
| <blockquote><p>The <code>utimbuf</code> structure is used with the <code>utime</code> function to |
| specify new access and modification times for a file. It contains the |
| following members: |
| |
| <dl> |
| <dt><code>time_t actime</code><dd>This is the access time for the file. |
| |
| <br><dt><code>time_t modtime</code><dd>This is the modification time for the file. |
| </dl> |
| </p></blockquote></div> |
| |
| <!-- time.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Function: int <b>utime</b> (<var>const char *filename, const struct utimbuf *times</var>)<var><a name="index-utime-1587"></a></var><br> |
| <blockquote><p>This function is used to modify the file times associated with the file |
| named <var>filename</var>. |
| |
| <p>If <var>times</var> is a null pointer, then the access and modification times |
| of the file are set to the current time. Otherwise, they are set to the |
| values from the <code>actime</code> and <code>modtime</code> members (respectively) |
| of the <code>utimbuf</code> structure pointed to by <var>times</var>. |
| |
| <p>The attribute modification time for the file is set to the current time |
| in either case (since changing the time stamps is itself a modification |
| of the file attributes). |
| |
| <p>The <code>utime</code> function returns <code>0</code> if successful and <code>-1</code> |
| on failure. In addition to the usual file name errors |
| (see <a href="File-Name-Errors.html#File-Name-Errors">File Name Errors</a>), the following <code>errno</code> error conditions |
| are defined for this function: |
| |
| <dl> |
| <dt><code>EACCES</code><dd>There is a permission problem in the case where a null pointer was |
| passed as the <var>times</var> argument. In order to update the time stamp on |
| the file, you must either be the owner of the file, have write |
| permission for the file, or be a privileged user. |
| |
| <br><dt><code>ENOENT</code><dd>The file doesn't exist. |
| |
| <br><dt><code>EPERM</code><dd>If the <var>times</var> argument is not a null pointer, you must either be |
| the owner of the file or be a privileged user. |
| |
| <br><dt><code>EROFS</code><dd>The file lives on a read-only file system. |
| </dl> |
| </p></blockquote></div> |
| |
| <p>Each of the three time stamps has a corresponding microsecond part, |
| which extends its resolution. These fields are called |
| <code>st_atime_usec</code>, <code>st_mtime_usec</code>, and <code>st_ctime_usec</code>; |
| each has a value between 0 and 999,999, which indicates the time in |
| microseconds. They correspond to the <code>tv_usec</code> field of a |
| <code>timeval</code> structure; see <a href="High_002dResolution-Calendar.html#High_002dResolution-Calendar">High-Resolution Calendar</a>. |
| |
| <p>The <code>utimes</code> function is like <code>utime</code>, but also lets you specify |
| the fractional part of the file times. The prototype for this function is |
| in the header file <samp><span class="file">sys/time.h</span></samp>. |
| <a name="index-sys_002ftime_002eh-1588"></a> |
| <!-- sys/time.h --> |
| <!-- BSD --> |
| |
| <div class="defun"> |
| — Function: int <b>utimes</b> (<var>const char *filename, struct timeval tvp</var><tt>[2]</tt>)<var><a name="index-utimes-1589"></a></var><br> |
| <blockquote><p>This function sets the file access and modification times of the file |
| <var>filename</var>. The new file access time is specified by |
| <var>tvp</var><code>[0]</code>, and the new modification time by |
| <var>tvp</var><code>[1]</code>. Similar to <code>utime</code>, if <var>tvp</var> is a null |
| pointer then the access and modification times of the file are set to |
| the current time. This function comes from BSD. |
| |
| <p>The return values and error conditions are the same as for the <code>utime</code> |
| function. |
| </p></blockquote></div> |
| |
| <!-- sys/time.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Function: int <b>lutimes</b> (<var>const char *filename, struct timeval tvp</var><tt>[2]</tt>)<var><a name="index-lutimes-1590"></a></var><br> |
| <blockquote><p>This function is like <code>utimes</code>, except that it does not follow |
| symbolic links. If <var>filename</var> is the name of a symbolic link, |
| <code>lutimes</code> sets the file access and modification times of the |
| symbolic link special file itself (as seen by <code>lstat</code>; |
| see <a href="Symbolic-Links.html#Symbolic-Links">Symbolic Links</a>) while <code>utimes</code> sets the file access and |
| modification times of the file the symbolic link refers to. This |
| function comes from FreeBSD, and is not available on all platforms (if |
| not available, it will fail with <code>ENOSYS</code>). |
| |
| <p>The return values and error conditions are the same as for the <code>utime</code> |
| function. |
| </p></blockquote></div> |
| |
| <!-- sys/time.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Function: int <b>futimes</b> (<var>int fd, struct timeval tvp</var><tt>[2]</tt>)<var><a name="index-futimes-1591"></a></var><br> |
| <blockquote><p>This function is like <code>utimes</code>, except that it takes an open file |
| descriptor as an argument instead of a file name. See <a href="Low_002dLevel-I_002fO.html#Low_002dLevel-I_002fO">Low-Level I/O</a>. This function comes from FreeBSD, and is not available on all |
| platforms (if not available, it will fail with <code>ENOSYS</code>). |
| |
| <p>Like <code>utimes</code>, <code>futimes</code> returns <code>0</code> on success and <code>-1</code> |
| on failure. The following <code>errno</code> error conditions are defined for |
| <code>futimes</code>: |
| |
| <dl> |
| <dt><code>EACCES</code><dd>There is a permission problem in the case where a null pointer was |
| passed as the <var>times</var> argument. In order to update the time stamp on |
| the file, you must either be the owner of the file, have write |
| permission for the file, or be a privileged user. |
| |
| <br><dt><code>EBADF</code><dd>The <var>filedes</var> argument is not a valid file descriptor. |
| |
| <br><dt><code>EPERM</code><dd>If the <var>times</var> argument is not a null pointer, you must either be |
| the owner of the file or be a privileged user. |
| |
| <br><dt><code>EROFS</code><dd>The file lives on a read-only file system. |
| </dl> |
| </p></blockquote></div> |
| |
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