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| Next: <a rel="next" accesskey="n" href="Reading-Attributes.html#Reading-Attributes">Reading Attributes</a>, |
| Up: <a rel="up" accesskey="u" href="File-Attributes.html#File-Attributes">File Attributes</a> |
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| |
| <h4 class="subsection">14.9.1 The meaning of the File Attributes</h4> |
| |
| <p><a name="index-status-of-a-file-1491"></a><a name="index-attributes-of-a-file-1492"></a><a name="index-file-attributes-1493"></a> |
| When you read the attributes of a file, they come back in a structure |
| called <code>struct stat</code>. This section describes the names of the |
| attributes, their data types, and what they mean. For the functions |
| to read the attributes of a file, see <a href="Reading-Attributes.html#Reading-Attributes">Reading Attributes</a>. |
| |
| <p>The header file <samp><span class="file">sys/stat.h</span></samp> declares all the symbols defined |
| in this section. |
| <a name="index-sys_002fstat_002eh-1494"></a> |
| <!-- sys/stat.h --> |
| <!-- POSIX.1 --> |
| |
| <div class="defun"> |
| — Data Type: <b>struct stat</b><var><a name="index-struct-stat-1495"></a></var><br> |
| <blockquote><p>The <code>stat</code> structure type is used to return information about the |
| attributes of a file. It contains at least the following members: |
| |
| <dl> |
| <dt><code>mode_t st_mode</code><dd>Specifies the mode of the file. This includes file type information |
| (see <a href="Testing-File-Type.html#Testing-File-Type">Testing File Type</a>) and the file permission bits |
| (see <a href="Permission-Bits.html#Permission-Bits">Permission Bits</a>). |
| |
| <br><dt><code>ino_t st_ino</code><dd>The file serial number, which distinguishes this file from all other |
| files on the same device. |
| |
| <br><dt><code>dev_t st_dev</code><dd>Identifies the device containing the file. The <code>st_ino</code> and |
| <code>st_dev</code>, taken together, uniquely identify the file. The |
| <code>st_dev</code> value is not necessarily consistent across reboots or |
| system crashes, however. |
| |
| <br><dt><code>nlink_t st_nlink</code><dd>The number of hard links to the file. This count keeps track of how |
| many directories have entries for this file. If the count is ever |
| decremented to zero, then the file itself is discarded as soon as no |
| process still holds it open. Symbolic links are not counted in the |
| total. |
| |
| <br><dt><code>uid_t st_uid</code><dd>The user ID of the file's owner. See <a href="File-Owner.html#File-Owner">File Owner</a>. |
| |
| <br><dt><code>gid_t st_gid</code><dd>The group ID of the file. See <a href="File-Owner.html#File-Owner">File Owner</a>. |
| |
| <br><dt><code>off_t st_size</code><dd>This specifies the size of a regular file in bytes. For files that are |
| really devices this field isn't usually meaningful. For symbolic links |
| this specifies the length of the file name the link refers to. |
| |
| <br><dt><code>time_t st_atime</code><dd>This is the last access time for the file. See <a href="File-Times.html#File-Times">File Times</a>. |
| |
| <br><dt><code>unsigned long int st_atime_usec</code><dd>This is the fractional part of the last access time for the file. |
| See <a href="File-Times.html#File-Times">File Times</a>. |
| |
| <br><dt><code>time_t st_mtime</code><dd>This is the time of the last modification to the contents of the file. |
| See <a href="File-Times.html#File-Times">File Times</a>. |
| |
| <br><dt><code>unsigned long int st_mtime_usec</code><dd>This is the fractional part of the time of the last modification to the |
| contents of the file. See <a href="File-Times.html#File-Times">File Times</a>. |
| |
| <br><dt><code>time_t st_ctime</code><dd>This is the time of the last modification to the attributes of the file. |
| See <a href="File-Times.html#File-Times">File Times</a>. |
| |
| <br><dt><code>unsigned long int st_ctime_usec</code><dd>This is the fractional part of the time of the last modification to the |
| attributes of the file. See <a href="File-Times.html#File-Times">File Times</a>. |
| |
| <!-- !!! st_rdev --> |
| <br><dt><code>blkcnt_t st_blocks</code><dd>This is the amount of disk space that the file occupies, measured in |
| units of 512-byte blocks. |
| |
| <p>The number of disk blocks is not strictly proportional to the size of |
| the file, for two reasons: the file system may use some blocks for |
| internal record keeping; and the file may be sparse—it may have |
| “holes” which contain zeros but do not actually take up space on the |
| disk. |
| |
| <p>You can tell (approximately) whether a file is sparse by comparing this |
| value with <code>st_size</code>, like this: |
| |
| <pre class="smallexample"> (st.st_blocks * 512 < st.st_size) |
| </pre> |
| <p>This test is not perfect because a file that is just slightly sparse |
| might not be detected as sparse at all. For practical applications, |
| this is not a problem. |
| |
| <br><dt><code>unsigned int st_blksize</code><dd>The optimal block size for reading of writing this file, in bytes. You |
| might use this size for allocating the buffer space for reading of |
| writing the file. (This is unrelated to <code>st_blocks</code>.) |
| </dl> |
| </p></blockquote></div> |
| |
| <p>The extensions for the Large File Support (LFS) require, even on 32-bit |
| machines, types which can handle file sizes up to 2^63. |
| Therefore a new definition of <code>struct stat</code> is necessary. |
| |
| <!-- sys/stat.h --> |
| <!-- LFS --> |
| <div class="defun"> |
| — Data Type: <b>struct stat64</b><var><a name="index-struct-stat64-1496"></a></var><br> |
| <blockquote><p>The members of this type are the same and have the same names as those |
| in <code>struct stat</code>. The only difference is that the members |
| <code>st_ino</code>, <code>st_size</code>, and <code>st_blocks</code> have a different |
| type to support larger values. |
| |
| <dl> |
| <dt><code>mode_t st_mode</code><dd>Specifies the mode of the file. This includes file type information |
| (see <a href="Testing-File-Type.html#Testing-File-Type">Testing File Type</a>) and the file permission bits |
| (see <a href="Permission-Bits.html#Permission-Bits">Permission Bits</a>). |
| |
| <br><dt><code>ino64_t st_ino</code><dd>The file serial number, which distinguishes this file from all other |
| files on the same device. |
| |
| <br><dt><code>dev_t st_dev</code><dd>Identifies the device containing the file. The <code>st_ino</code> and |
| <code>st_dev</code>, taken together, uniquely identify the file. The |
| <code>st_dev</code> value is not necessarily consistent across reboots or |
| system crashes, however. |
| |
| <br><dt><code>nlink_t st_nlink</code><dd>The number of hard links to the file. This count keeps track of how |
| many directories have entries for this file. If the count is ever |
| decremented to zero, then the file itself is discarded as soon as no |
| process still holds it open. Symbolic links are not counted in the |
| total. |
| |
| <br><dt><code>uid_t st_uid</code><dd>The user ID of the file's owner. See <a href="File-Owner.html#File-Owner">File Owner</a>. |
| |
| <br><dt><code>gid_t st_gid</code><dd>The group ID of the file. See <a href="File-Owner.html#File-Owner">File Owner</a>. |
| |
| <br><dt><code>off64_t st_size</code><dd>This specifies the size of a regular file in bytes. For files that are |
| really devices this field isn't usually meaningful. For symbolic links |
| this specifies the length of the file name the link refers to. |
| |
| <br><dt><code>time_t st_atime</code><dd>This is the last access time for the file. See <a href="File-Times.html#File-Times">File Times</a>. |
| |
| <br><dt><code>unsigned long int st_atime_usec</code><dd>This is the fractional part of the last access time for the file. |
| See <a href="File-Times.html#File-Times">File Times</a>. |
| |
| <br><dt><code>time_t st_mtime</code><dd>This is the time of the last modification to the contents of the file. |
| See <a href="File-Times.html#File-Times">File Times</a>. |
| |
| <br><dt><code>unsigned long int st_mtime_usec</code><dd>This is the fractional part of the time of the last modification to the |
| contents of the file. See <a href="File-Times.html#File-Times">File Times</a>. |
| |
| <br><dt><code>time_t st_ctime</code><dd>This is the time of the last modification to the attributes of the file. |
| See <a href="File-Times.html#File-Times">File Times</a>. |
| |
| <br><dt><code>unsigned long int st_ctime_usec</code><dd>This is the fractional part of the time of the last modification to the |
| attributes of the file. See <a href="File-Times.html#File-Times">File Times</a>. |
| |
| <!-- !!! st_rdev --> |
| <br><dt><code>blkcnt64_t st_blocks</code><dd>This is the amount of disk space that the file occupies, measured in |
| units of 512-byte blocks. |
| |
| <br><dt><code>unsigned int st_blksize</code><dd>The optimal block size for reading of writing this file, in bytes. You |
| might use this size for allocating the buffer space for reading of |
| writing the file. (This is unrelated to <code>st_blocks</code>.) |
| </dl> |
| </p></blockquote></div> |
| |
| <p>Some of the file attributes have special data type names which exist |
| specifically for those attributes. (They are all aliases for well-known |
| integer types that you know and love.) These typedef names are defined |
| in the header file <samp><span class="file">sys/types.h</span></samp> as well as in <samp><span class="file">sys/stat.h</span></samp>. |
| Here is a list of them. |
| |
| <!-- sys/types.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Data Type: <b>mode_t</b><var><a name="index-mode_005ft-1497"></a></var><br> |
| <blockquote><p>This is an integer data type used to represent file modes. In the |
| GNU system, this is equivalent to <code>unsigned int</code>. |
| </p></blockquote></div> |
| |
| <p><a name="index-inode-number-1498"></a><!-- sys/types.h --> |
| <!-- POSIX.1 --> |
| |
| <div class="defun"> |
| — Data Type: <b>ino_t</b><var><a name="index-ino_005ft-1499"></a></var><br> |
| <blockquote><p>This is an arithmetic data type used to represent file serial numbers. |
| (In Unix jargon, these are sometimes called <dfn>inode numbers</dfn>.) |
| In the GNU system, this type is equivalent to <code>unsigned long int</code>. |
| |
| <p>If the source is compiled with <code>_FILE_OFFSET_BITS == 64</code> this type |
| is transparently replaced by <code>ino64_t</code>. |
| </p></blockquote></div> |
| |
| <!-- sys/types.h --> |
| <!-- Unix98 --> |
| <div class="defun"> |
| — Data Type: <b>ino64_t</b><var><a name="index-ino64_005ft-1500"></a></var><br> |
| <blockquote><p>This is an arithmetic data type used to represent file serial numbers |
| for the use in LFS. In the GNU system, this type is equivalent to |
| <code>unsigned long long int</code>. |
| |
| <p>When compiling with <code>_FILE_OFFSET_BITS == 64</code> this type is |
| available under the name <code>ino_t</code>. |
| </p></blockquote></div> |
| |
| <!-- sys/types.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Data Type: <b>dev_t</b><var><a name="index-dev_005ft-1501"></a></var><br> |
| <blockquote><p>This is an arithmetic data type used to represent file device numbers. |
| In the GNU system, this is equivalent to <code>int</code>. |
| </p></blockquote></div> |
| |
| <!-- sys/types.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Data Type: <b>nlink_t</b><var><a name="index-nlink_005ft-1502"></a></var><br> |
| <blockquote><p>This is an arithmetic data type used to represent file link counts. |
| In the GNU system, this is equivalent to <code>unsigned short int</code>. |
| </p></blockquote></div> |
| |
| <!-- sys/types.h --> |
| <!-- Unix98 --> |
| <div class="defun"> |
| — Data Type: <b>blkcnt_t</b><var><a name="index-blkcnt_005ft-1503"></a></var><br> |
| <blockquote><p>This is an arithmetic data type used to represent block counts. |
| In the GNU system, this is equivalent to <code>unsigned long int</code>. |
| |
| <p>If the source is compiled with <code>_FILE_OFFSET_BITS == 64</code> this type |
| is transparently replaced by <code>blkcnt64_t</code>. |
| </p></blockquote></div> |
| |
| <!-- sys/types.h --> |
| <!-- Unix98 --> |
| <div class="defun"> |
| — Data Type: <b>blkcnt64_t</b><var><a name="index-blkcnt64_005ft-1504"></a></var><br> |
| <blockquote><p>This is an arithmetic data type used to represent block counts for the |
| use in LFS. In the GNU system, this is equivalent to <code>unsigned |
| long long int</code>. |
| |
| <p>When compiling with <code>_FILE_OFFSET_BITS == 64</code> this type is |
| available under the name <code>blkcnt_t</code>. |
| </p></blockquote></div> |
| |
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