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<title>ftruncate()--Truncate File</title>
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<h2>ftruncate()--Truncate File</h2>
<div class="box" style="width: 70%;">
<br>
&nbsp;&nbsp;Syntax<br>
<pre>
#include &lt;unistd.h&gt;
int ftruncate(int <em>file_descriptor</em>, off_t <em>length</em>);
</pre>
&nbsp;&nbsp;Service Program Name: QP0LLIB1<br>
<!-- iddvc RMBR -->
<br>
&nbsp;&nbsp;Default Public Authority: *USE<br>
<!-- iddvc RMBR -->
<br>
&nbsp;&nbsp;Threadsafe: Conditional; see <a href="#HDRFTRNUSG">Usage Notes</a>.<br>
<!-- iddvc RMBR -->
<br>
</div>
<p>The <strong>ftruncate()</strong> function truncates the file indicated by
the open file descriptor <em>file_descriptor</em> to the indicated <em>
length</em>. <em>file_descriptor</em> must be a "regular file" that is open for
writing. (A regular file is a stream file that can support positioning the file
offset.) If the file size exceeds <em>length</em>, any extra data is discarded.
If the file size is smaller than <em>length</em>, the file is extended and
filled with binary zeros to the indicated length. (In the QSYS.LIB and
independent ASP QSYS.LIB file systems blanks are used instead of zeros to pad
records after a member is extended.)
The <strong>ftruncate()</strong> function does not modify the current file offset
for any open file descriptions associated with the file.
</p>
<p>If <strong>ftruncate()</strong> completes successfully, it marks the change
time and modification times of the file. Also, the S_ISUID (set-user-ID) and
S_ISGID (set-group-ID) bits of the file mode are cleared. If <strong>
ftruncate()</strong> is not successful, the file is unchanged.</p>
<p>If <strong>ftruncate()</strong> is used to truncate the file to 0 bytes and
the file has a digital signature, the signature is deleted.</p>
<br>
<h3>Parameters</h3>
<dl>
<dt><strong><em>file_descriptor</em></strong></dt>
<dd>(Input) The file descriptor of the file.<br>
<br>
</dd>
<dt><strong><em>length</em></strong></dt>
<dd>(Input) The desired size of the file in bytes.</dd>
</dl>
<br>
<h3>Authorities</h3>
<p>No authorization is required. Authorization is verified during <strong>
open()</strong> or <strong>creat()</strong>.</p>
<br>
<h3>Return Value</h3>
<dl>
<dt><em>0</em></dt>
<dd><strong>ftruncate()</strong> was successful.</dd>
<dt><em>-1</em></dt>
<dd><strong>ftruncate()</strong> was not successful. The <em>errno</em> global
variable is set to indicate the error. If the file descriptor is not open for
writing, <strong>ftruncate</strong> returns a [EBADF] error. If the file
descriptor is a valid descriptor open for writing but is not a descriptor for a
regular file, <strong>ftruncate()</strong> returns a [EINVAL] error.</dd>
</dl>
<br>
<h3><a name="HDRFTRNERR">Error Conditions</a></h3>
<p>If <strong>ftruncate()</strong> is not successful, <em>errno</em> usually
indicates one of the following errors. Under some conditions, <em>errno</em>
could indicate an error other than those listed here.</p>
<table cellpadding="5">
<!-- cols="25 75" -->
<tr>
<th align="left" valign="bottom">Error condition</th>
<th align="left" valign="bottom">Additional information</th>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EACCES">EACCES</a>]</em></td>
<td align="left" valign="top">
<p>If you are accessing a remote file through the Network File System, update
operations to file permissions at the server are not reflected at the client
until updates to data that is stored locally by the Network File System take
place. (Several options on the Add Mounted File System (ADDMFS) command
determine the time between refresh operations of local data.) Access to a
remote file may also fail due to different mappings of user IDs (UID) or group
IDs (GID) on the local and remote systems.</p>
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EAGAIN">EAGAIN</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EBADF">EBADF</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EBADFID">EBADFID</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EBADNAME">EBADNAME</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EBUSY">EBUSY</a>]</em></td>
<td align="left" valign="top">
<p>The QSYS.LIB or independent ASP QSYS.LIB file system cannot get exclusive
access to the member to clear truncated data.</p>
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ECONVERT">ECONVERT</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EDAMAGE">EDAMAGE</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EFBIG">EFBIG</a>]</em></td>
<td align="left" valign="top">
<p>The size of the object would exceed the system allowed maximum size or the
process soft file size limit.
The file is a regular file and <em>length</em> is greater than 2GB minus 1
byte.</p>
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EINTR">EINTR</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EINVAL">EINVAL</a>]</em></td>
<td align="left" valign="top">
<p>For example, <em>file_descriptor</em>
does not refer to a regular file open for writing, or the
specified length is not correct.</p>
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EIO">EIO</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EISDIR">EISDIR</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EJRNDAMAGE">EJRNDAMAGE</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EJRNENTTOOLONG">EJRNENTTOOLONG</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EJRNINACTIVE">EJRNINACTIVE</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EJRNRCVSPC">EJRNRCVSPC</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr><tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ELOCKED">ELOCKED</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENAMETOOLONG">ENAMETOOLONG</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENEWJRN">ENEWJRN</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENEWJRNRCV">ENEWJRNRCV</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENOENT">ENOENT</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENOMEM">ENOMEM</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENOSPC">ENOSPC</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENOSYS">ENOSYS</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENOSYSRSC">ENOSYSRSC</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENOTAVAIL">ENOTAVAIL</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENOTDIR">ENOTDIR</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENOTSAFE">ENOTSAFE</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENOTSUP">ENOTSUP</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EROOBJ">EROOBJ</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ESTALE">ESTALE</a>]</em></td>
<td align="left" valign="top">
<p>If you are accessing a remote file through the Network File System, the file
may have been deleted at the server.</p>
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EUNKNOWN">EUNKNOWN</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
</table>
<p>If interaction with a file server is required to access the object, <em>
errno</em> could also indicate one of the following errors:</p>
<table cellpadding="5">
<!-- cols="25 75" -->
<tr>
<th align="left" valign="bottom">Error condition</th>
<th align="left" valign="bottom">Additional information</th>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EADDRNOTAVAIL">EADDRNOTAVAIL</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ECONNABORTED">ECONNABORTED</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ECONNREFUSED">ECONNREFUSED</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ECONNRESET">ECONNRESET</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EHOSTDOWN">EHOSTDOWN</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EHOSTUNREACH">EHOSTUNREACH</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENETDOWN">ENETDOWN</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENETRESET">ENETRESET</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ENETUNREACH">ENETUNREACH</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#ETIMEDOUT">ETIMEDOUT</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
<tr>
<td align="left" valign="top">
<em>[<a href="unix14.htm#EUNATCH">EUNATCH</a>]</em></td>
<td align="left" valign="top">
&nbsp;
</td>
</tr>
</table>
<br>
<br>
<h3>Error Messages</h3>
<p>The following messages may be sent from this function:</p>
<table width="100%">
<tr>
<td width="15%" valign="top">CPE3418 E</td>
<td width="85%" valign="top">Possible APAR condition or hardware failure.</td>
</tr>
<tr>
<td valign="top">CPFA0D4 E</td>
<td valign="top">File system error occurred. Error number &amp;1.</td>
</tr>
<tr>
<td valign="top">CPF3CF2 E</td>
<td valign="top">Error(s) occurred during running of &amp;1 API.</td>
</tr>
<tr>
<td valign="top">CPF9872 E</td>
<td valign="top">Program or service program &amp;1 in library &amp;2 ended.
Reason code &amp;3.</td>
</tr>
</table>
<br>
<h3><a name="HDRFTRNUSG">Usage Notes</a></h3>
<ol type="1">
<li>This function will fail with error code [ENOTSAFE] when all the following
conditions are true:<br>
<br>
<ul>
<li>Where multiple threads exist in the job.<br>
<br>
</li>
<li>The object on which this function is operating resides in a file system
that is not threadsafe. Only the following file systems are threadsafe for this
function:<br>
<br>
<ul>
<li>"Root" (/)</li>
<li>QOpenSys</li>
<li>User-defined</li>
<li>QNTC</li>
<li>QSYS.LIB</li>
<li>Independent ASP QSYS.LIB</li>
<li>QOPT</li>
<li>Network File System</li>
<li>QFileSvr.400</li>
</ul>
</li>
</ul>
<br>
<br>
</li>
<li>When you develop in C-based languages and this function is compiled with
_LARGE_FILES defined, it will be mapped to <strong>ftruncate64()</strong>. Note
also that the type of the <em>length</em> parameter will be remapped from off_t
to off64_t.<br>
<br>
</li>
<li>For the Network File System, this function will fail with the [EFBIG] or
the [EIO] error if the length specified is greater than the largest file size
supported by the server.<br>
<br>
</li>
<li>Using this function on a character special file results in a return value
of -1 and the errno global value set to EINVAL.<br>
<br>
</li>
<li>QSYS.LIB and Independent ASP QSYS.LIB File System Differences
<p>This function is not supported for save files and will fail with error code
[ENOTSUP].</p>
</li>
<li>If the request exceeds the process soft file size limit, signal SIFXFSZ is
issued.</li>
</ol>
<br>
<h3>Related Information</h3>
<ul>
<li>The &lt;<strong>unistd.h</strong>&gt; file (see <a href="unix13.htm">Header
Files for UNIX-Type Functions</a>)<br>
</li>
<li><a href="ftrunc64.htm">ftruncate64()</a>--Truncate File (Large File
Enabled)<br>
</li>
<li><a href="open.htm">open()</a>--Open File</li>
</ul>
<br>
<h3>Example</h3>
<p>See <a href="../apiref/aboutapis.htm#codedisclaimer">Code disclaimer information</a>
for information pertaining to code examples.</p>
<p>The following example uses <strong>ftruncate()</strong>:</p>
<pre>
#include &lt;unistd.h&gt;
#include &lt;sys/types.h&gt;
#include &lt;sys/stat.h&gt;
#include &lt;fcntl.h&gt;
#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
#define string_len 1000
main() {
char *mega_string;
int file_descriptor;
int ret;
char fn[]="write.file";
struct stat st;
if ((mega_string = (char*) malloc(string_len)) == NULL)
perror("malloc() error");
else if ((file_descriptor = creat(fn, S_IWUSR)) &lt; 0)
perror("creat() error");
else {
memset(mega_string, '0', string_len);
if ((ret = write(file_descriptor, mega_string, string_len)) == -1)
perror("write() error");
else {
printf("write() wrote %d bytes\n", ret);
fstat(file_descriptor, &amp;st);
printf("the file has %ld bytes\n", (long) st.st_size);
if (ftruncate(file_descriptor, 1) != 0)
perror("ftruncate() error");
else {
fstat(file_descriptor, &amp;st);
printf("the file has %ld bytes\n", (long) st.st_size);
}
}
close(file_descriptor);
unlink(fn);
}
free(mega_string);
}
</pre>
<p><strong>Output:</strong></p>
<pre>
write() wrote 1000 bytes
the file has 1000 bytes
the file has 1 bytes
</pre>
<br>
<hr>
API introduced: V3R1
<hr>
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