php-doc-en/reference/filesystem/functions/fwrite.xml

<?xml version="1.0" encoding="utf-8"?>
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<refentry xmlns="http://docbook.org/ns/docbook" xml:id="function.fwrite">
 <refnamediv>
  <refname>fwrite</refname>
  <refpurpose>Binary-safe file write</refpurpose>
 </refnamediv>
 
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>int</type><methodname>fwrite</methodname>
   <methodparam><type>resource</type><parameter>handle</parameter></methodparam>
   <methodparam><type>string</type><parameter>string</parameter></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>length</parameter></methodparam>
  </methodsynopsis>
  <simpara>
   <function>fwrite</function> writes the contents of
   <parameter>string</parameter> to the file stream pointed to by
   <parameter>handle</parameter>. 
  </simpara>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>handle</parameter></term>
     <listitem>
      &fs.file.pointer;
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>string</parameter></term>
     <listitem>
      <para>
       The string that is to be written.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>length</parameter></term>
     <listitem>
      <para>
       If the <parameter>length</parameter> argument is given, writing will
       stop after <parameter>length</parameter> bytes have been written or
       the end of <parameter>string</parameter> is reached, whichever comes
       first.
      </para>
      <para>
       Note that if the <parameter>length</parameter> argument is given,
       then the <link
       linkend="ini.magic-quotes-runtime">magic_quotes_runtime</link>
       configuration option will be ignored and no slashes will be
       stripped from <parameter>string</parameter>.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <simpara>
   <function>fwrite</function> returns the number of bytes
   written, or &false; on error.
  </simpara>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  <note>
   <para>
    Writing to a network stream may end before the whole string is written.
    Return value of <function>fwrite</function> may be checked:
    <programlisting role="php">
<![CDATA[
<?php
function fwrite_stream($fp, $string) {
    for ($written = 0; $written < strlen($string); $written += $fwrite) {
        $fwrite = fwrite($fp, substr($string, $written));
        if ($fwrite === false) {
            return $written;
        }
    }
    return $written;
}
?>
]]>
    </programlisting>
   </para>
  </note>
  
  <note>
   <para>
    On systems which differentiate between binary and text files
    (i.e. Windows) the file must be opened with 'b' included in
    <function>fopen</function> mode parameter.
   </para>
  </note>
  <note>
   <para>
    If <parameter>handle</parameter> was <function>fopen</function>ed in
    append mode, <function>fwrite</function>s are atomic (unless the size of
    <parameter>string</parameter> exceeds the filesystem's block size, on some
    platforms, and as long as the file is on a local filesystem). That is,
    there is no need to <function>flock</function> a resource before calling
    <function>fwrite</function>; all of the data will be written without
    interruption.
   </para>
  </note>
  <note>
   <para>
    If writing twice to the file pointer, then the data will be appended to 
    the end of the file content:
        <programlisting role="php">
<![CDATA[
<?php
$fp = fopen('data.txt', 'w');
fwrite($fp, '1');
fwrite($fp, '23');
fclose($fp);

// the content of 'data.txt' is now 123 and not 23!
?>
]]>
        </programlisting>
   </para>
  </note>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title>A simple <function>fwrite</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
$filename = 'test.txt';
$somecontent = "Add this to the file\n";

// Let's make sure the file exists and is writable first.
if (is_writable($filename)) {

    // In our example we're opening $filename in append mode.
    // The file pointer is at the bottom of the file hence
    // that's where $somecontent will go when we fwrite() it.
    if (!$handle = fopen($filename, 'a')) {
         echo "Cannot open file ($filename)";
         exit;
    }

    // Write $somecontent to our opened file.
    if (fwrite($handle, $somecontent) === FALSE) {
        echo "Cannot write to file ($filename)";
        exit;
    }

    echo "Success, wrote ($somecontent) to file ($filename)";

    fclose($handle);

} else {
    echo "The file $filename is not writable";
}
?>
]]>
    </programlisting>
   </example>
  </para>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>fread</function></member>
    <member><function>fopen</function></member>
    <member><function>fsockopen</function></member>
    <member><function>popen</function></member>
    <member><function>file_get_contents</function></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>

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