php-doc-en/functions/array.sgml

 <reference id="ref.array">
  <title>Array functions</title>
  <titleabbrev>Arrays</titleabbrev>

  <refentry id="function.array">
   <refnamediv>
    <refname>array</refname>
    <refpurpose>
     Create an array
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>array <function>array</function></funcdef>
     <varargs>
    </funcsynopsis>
    <para>
     Returns an array of the parameters.  The parameters can be given
     an index with the <literal>=&gt;</literal> operator.

    <note>
     <para>
      <function>array</function> is a language construct used to
      represent literal arrays, and not a regular function.
     </para>
    </note></para>

    <para>
     The following example demonstrates how to create a
     two-dimensional array, how to specify keys for associative
     arrays, and how to skip-and-continue numeric indices in normal
     arrays.

     <example>
      <title><function>array</function> example</title>
      <programlisting>
$fruits = array(
    "fruits"  => array("a"=>"orange","b"=>"banana","c"=>"apple"),
    "numbers" => array(1, 2, 3, 4, 5, 6),
    "holes"   => array("first", 5 => "second", "third")
);
</programlisting></example></para>

    <para>
     See also:
     <function>list</function>.</para>
   </refsect1>
  </refentry>

  <refentry id="function.array-count-values">
   <refnamediv>
    <refname>array_count_values</refname>
    <refpurpose>Counts all the values of an array</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>array <function>array_count_values</function></funcdef>
     <paramdef>array <parameter>input</parameter></paramdef>
    </funcsynopsis>

    <para>
     <function>array_count_values</function> returns an array using the values 
	 of the <parameter>input</parameter> array as keys and their frequency in 
	 <parameter>input</parameter> as values.</para>

    <para>
     <example>
      <title><function>array_count_values</function> example</title>
      <programlisting>
$array = array(1,"hello",1,"world","hello");
array_count_values($array);       // returns array(1=>2, "hello"=>2, "world"=>1)
      </programlisting>
     </example>

    <note>
     <para>
      This function was added in PHP 4.0.</para> 
    </note></para>
   </refsect1>
  </refentry>

  <refentry id="function.array-flip">
   <refnamediv>
    <refname>array_flip</refname>
    <refpurpose>Flip all the values of an array</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>array <function>array_flip</function></funcdef>
     <paramdef>array <parameter>trans</parameter></paramdef>
    </funcsynopsis>

    <para>
     <function>array_flip</function> returns an array in flip order.
    </para>
    <para>
     <example>
      <title><function>array_flip</function> example</title>
      <programlisting role="php">
$trans = array_flip ($trans);
$original = strtr ($str, $trans);
      </programlisting>
     </example>

     <note>
      <para>
       This function was added in PHP 4.0.
      </para> 
     </note></para>

   </refsect1>
  </refentry>

  <refentry id="function.array-keys">
   <refnamediv>
    <refname>array_keys</refname>
    <refpurpose>Return all the keys of an array</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>array <function>array_keys</function></funcdef>
     <paramdef>array <parameter>input</parameter></paramdef>
     <paramdef>mixed
     <parameter><optional>search_value</optional></parameter></paramdef>
    </funcsynopsis>

    <para>
     <function>array_keys</function> returns the keys, numeric and
     string, from the <parameter>input</parameter> array.</para>

    <para>
     If the optional <parameter>search_value</parameter> is specified,
     then only the keys for that value are returned. Otherwise, all
     the keys from the <parameter>input</parameter> are returned.</para>

    <para>
     <example>
      <title><function>array_keys</function> example</title>
      <programlisting>
$array = array(0 => 100, "color" => "red");
array_keys($array);       // returns array(0, "color")

$array = array(1, 100, 2, 100);
array_keys($array, 100); //  returns array(0, 2) 
      </programlisting>
     </example></para>

    <para>
     See also <function>array_values</function>.

    <note>
     <para>
      This function was added in PHP 4.0.</para> 
    </note></para>
   </refsect1>
  </refentry>

  <refentry id="function.array-merge">
   <refnamediv>
    <refname>array_merge</refname>
    <refpurpose>Merge two or more arrays</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>array <function>array_merge</function></funcdef>
     <paramdef>array <parameter>array1</parameter></paramdef>
     <paramdef>array <parameter>array2</parameter></paramdef>
     <paramdef>
      <parameter><optional> ...</optional></parameter>
     </paramdef>
    </funcsynopsis>

    <para>
     <function>array_merge</function> merges the elements of two or
     more arrays together so that the values of one are appended to
     the end of the previous one.  It returns the resulting array.</para>

    <para>
     If the input arrays had the same string keys, then the later
     value for that key will overwrite previous one.  If, however, the
     arrays have the same numeric key, this does not happen since the
     values are appended.</para>

    <para>
     <example>
      <title><function>array_merge</function> example</title>
      <programlisting>
$array1 = array("color" => "red", 2, 4);
$array2 = array("a", "b", "color" => "green", "shape" => "trapezoid");
array_merge($array1, $array2);
      </programlisting>
      <para>
       Resulting array will be array("color" => "green", 2, 4, "a",
       "b", "shape" => "trapezoid").</para>
     </example>

    <note>
     <para>
      This function was added in PHP 4.0.</para>
    </note></para>
   </refsect1>
  </refentry>

  <refentry id="function.array-pad">
   <refnamediv>
    <refname>array_pad</refname>
    <refpurpose>Pad array to the specified length with a value</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>array <function>array_pad</function></funcdef>
     <paramdef>array <parameter>input</parameter></paramdef>
     <paramdef>int <parameter>pad_size</parameter></paramdef>
     <paramdef>mixed <parameter>pad_value</parameter></paramdef>
    </funcsynopsis>

    <para>
     <function>array_pad</function> returns a copy of the
     <parameter>input</parameter> padded to size specified by
     <parameter>pad_size</parameter> with value
     <parameter>pad_value</parameter>. If
     <parameter>pad_size</parameter> is positive then the array is
     padded on the right, if it's negative then on the left. If the
     absolute value of <parameter>pad_size</parameter> is less than or
     equal to the length of the <parameter>input</parameter> then no
     padding takes place.
    </para>

    <para>
     <example>
      <title><function>array_pad</function> example</title>
      <programlisting>
$input = array(12, 10, 9);

$result = array_pad($input, 5, 0);
// result is array(12, 10, 9, 0, 0)

$result = array_pad($input, -7, -1);
// result is array(-1, -1, -1, -1, 12, 10, 9)

$result = array_pad($input, 2, "noop");
// not padded
      </programlisting>
     </example>
    </para>
   </refsect1>
  </refentry>

  <refentry id="function.array-pop">
   <refnamediv>
    <refname>array_pop</refname>
    <refpurpose>Pop the element off the end of array</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>mixed <function>array_pop</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>

    <para>
     <function>array_pop</function> pops and returns the last value of
     the <parameter>array</parameter>, shortening the
     <parameter>array</parameter> by one element.</para>

    <para>
     <example>
      <title><function>array_pop</function> example</title>
      <programlisting>
$stack = array("orange", "apple", "raspberry");
$fruit = array_pop($stack);
      </programlisting>
      <para>
       After this, $stack has only 2 elements: "orange" and "apple",
       and $fruit has "raspberry".</para>
     </example></para>

    <para>
     See also <function>array_push</function>,
     <function>array_shift</function>, and
     <function>array_unshift</function>.

    <note>
     <para>
      This function was added in PHP 4.0.</para> 
    </note></para>
   </refsect1>
  </refentry>

  <refentry id="function.array-push">
   <refnamediv>
    <refname>array_push</refname>
    <refpurpose>
     Push one or more elements onto the end of array
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>int <function>array_push</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
     <paramdef>mixed <parameter>var</parameter></paramdef>
     <paramdef><parameter><optional>...</optional></parameter></paramdef>
    </funcsynopsis>

    <para>
     <function>array_push</function> treats
     <parameter>array</parameter> as a stack, and pushes the passed
     variables onto the end of <parameter>array</parameter>. The
     length of <parameter>array</parameter> increases by the number of
     variables pushed. Has the same effect as:
     <programlisting>
$array[] = $var;
     </programlisting>
     repeated for each <parameter>var</parameter>.</para>

    <para>
     Returns the new number of elements in the array.</para>

    <para>
     <example>
      <title><function>array_push</function> example</title>
      <programlisting>
$stack = array(1, 2);
array_push($stack, "+", 3);
      </programlisting>
     </example>
     This example would result in $stack having 4 elements: 1, 2, "+",
     and 3.</para>

    <para>
     See also: 
     <function>array_pop</function>,
     <function>array_shift</function>, and
     <function>array_unshift</function>.

    <note>
     <para>
      This function was added in PHP 4.0.</para> 
    </note></para>
   </refsect1>
  </refentry>

  <refentry id="function.array-reverse">
   <refnamediv>
    <refname>array_reverse</refname>
    <refpurpose>Return an array with elements in reverse order</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>array <function>array_reverse</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>

    <para>
     <function>array_reverse</function> takes input <parameter>array</parameter> and returns a new array with the order of the elements reversed.</para>

    <para>
     <example>
      <title><function>array_reverse</function> example</title>
      <programlisting>
$input = array("php", 4.0, array("green", "red"));
$result = array_reverse($input);
      </programlisting>
     </example>
     This makes $result have array(array("green", "red"), 4.0, "php").

     <note>
      <para>
       This function was added in PHP 4.0 Beta 3.</para>
     </note></para>
   </refsect1>
  </refentry>

  <refentry id="function.array-shift">
   <refnamediv>
    <refname>array_shift</refname>
    <refpurpose>Pop an element off the beginning of array</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>mixed <function>array_shift</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>

    <para>
     <function>array_shift</function> shifts the first value of the
     <parameter>array</parameter> off and returns it, shortening the
     <parameter>array</parameter> by one element and moving everything
     down.</para>

    <para>
     <example>
      <title><function>array_shift</function> example</title>
      <programlisting>
$args = array("-v", "-f");
$opt = array_shift($args);
      </programlisting>
     </example>
     This would result in $args having one element "-f" left, and $opt
     being "-v".</para>

    <para>
     See also <function>array_unshift</function>,
     <function>array_push</function>, and
     <function>array_pop</function>.

    <note>
     <para>
      This function was added in PHP 4.0.</para> 
    </note></para>
   </refsect1>
  </refentry>

  <refentry id="function.array-slice">
   <refnamediv>
    <refname>array_slice</refname>
    <refpurpose>Extract a slice of the array</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>array <function>array_slice</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
     <paramdef>int <parameter>offset</parameter></paramdef>
     <paramdef>int
      <parameter>
       <optional>length</optional>
      </parameter>
     </paramdef>
    </funcsynopsis>

    <para>
     <function>array_slice</function> returns a sequence of elements
     from the <parameter>array</parameter> specified by the
     <parameter>offset</parameter> and <parameter>length</parameter>
     parameters.</para>

    <para>
     If <parameter>offset</parameter> is positive, the sequence will
     start at that offset in the <parameter>array</parameter>.  If
     <parameter>offset</parameter> is negative, the sequence will
     start that far from the end of the <parameter>array</parameter>.</para>

    <para>
     If <parameter>length</parameter> is given and is positive, then
     the sequence will have that many elements in it. If
     <parameter>length</parameter> is given and is negative then the
     sequence will stop that many elements from the end of the
     array. If it is omitted, then the sequence will have everything
     from <parameter>offset</parameter> up until the end of the
     <parameter>array</parameter>.</para>

    <para>
     <example>
      <title><function>array_slice</function> examples</title>
      <programlisting>
$input = array("a", "b", "c", "d", "e");

$output = array_slice($input, 2);      // returns "c", "d", and "e"
$output = array_slice($input, 2, -1);  // returns "c", "d"
$output = array_slice($input, -2, 1);  // returns "d"
$output = array_slice($input, 0, 3);   // returns "a", "b", and "c"
      </programlisting>
     </example></para>

    <para>
     See also <function>array_splice</function>.

    <note>
     <para>
      This function was added in PHP 4.0.</para> 
    </note></para>     
   </refsect1>
  </refentry>

  <refentry id="function.array-splice">
   <refnamediv>
    <refname>array_splice</refname>
    <refpurpose>
     Remove a portion of the array and replace it with something
     else
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>array <function>array_splice</function></funcdef>
     <paramdef>array <parameter>input</parameter></paramdef>
     <paramdef>int <parameter>offset</parameter></paramdef>
     <paramdef>int
      <parameter><optional>length</optional></parameter>
     </paramdef>
     <paramdef>array
     <parameter><optional>replacement</optional></parameter></paramdef>
    </funcsynopsis>

    <para>
     <function>array_splice</function> removed the elements designated
     by <parameter>offset</parameter> and
     <parameter>length</parameter> from the
     <parameter>input</parameter> array, and replaces them with the
     elements of the <parameter>replacement</parameter> array, if
     supplied.</para>

    <para>
     If <parameter>offset</parameter> is positive then the start of
     removed portion is at that offset from the beginning of the
     <parameter>input</parameter> array.  If
     <parameter>offset</parameter> is negative then it starts that far
     from the end of the <parameter>input</parameter> array.</para>

    <para>
     If <parameter>length</parameter> is omitted, removes everything
     from <parameter>offset</parameter> to the end of the array.  If
     <parameter>length</parameter> is specified and is positive, then
     that many elements will be removed. If
     <parameter>length</parameter> is specified and is negative then
     the end of the removed portion will be that many elements from
     the end of the array.  Tip: to remove everything from
     <parameter>offset</parameter> to the end of the array when
     <parameter>replacement</parameter> is also specified, use
     <literal>count($input)</literal> for
     <parameter>length</parameter>.</para>

    <para>
     If <parameter>replacement</parameter> array is specified, then
     the removed elements are replaced with elements from this array.
     If <parameter>offset</parameter> and
     <parameter>length</parameter> are such that nothing is removed,
     then the elements from the <parameter>replacement</parameter>
     array are inserted in the place specified by the
     <parameter>offset</parameter>. Tip: if the replacement is just
     one element it is not necessary to put <literal>array()</literal>
     around it, unless the element is an array itself.</para>

    <para>
     The following equivalences hold:
     <programlisting>
array_push($input, $x, $y)     array_splice($input, count($input), 0, array($x, $y))
array_pop($input)              array_splice($input, -1)
array_shift($input)            array_splice($input, 0, 1)
array_unshift($input, $x, $y)  array_splice($input, 0, 0, array($x, $y))
$a[$x] = $y                    array_splice($input, $x, 1, $y)
     </programlisting></para>

    <para>
     Returns the array consisting of removed elements.</para>

    <para>
     <example>
      <title><function>array_splice</function> examples</title>
      <programlisting>
$input = array("red", "green", "blue", "yellow");

array_splice($input, 2);      // $input is now array("red", "green")
array_splice($input, 1, -1);  // $input is now array("red", "yellow")
array_splice($input, 1, count($input), "orange");  
                              // $input is now array("red", "orange")
array_splice($input, -1, 1, array("black", "maroon")); 
                              // $input is now array("red", "green", 
                              //          "blue", "black", "maroon")
      </programlisting>
     </example></para>

    <para>
     See also <function>array_slice</function>.

    <note>
     <para>
      This function was added in PHP 4.0.</para> 
    </note></para>
   </refsect1>
  </refentry>

  <refentry id="function.array-unshift">
   <refnamediv>
    <refname>array_unshift</refname>
    <refpurpose>Push one or more elements
     onto the beginning of array</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcprototype>
      <funcdef>int <function>array_unshift</function></funcdef>
      <paramdef>array <parameter>array</parameter></paramdef>
      <paramdef>mixed <parameter>var</parameter></paramdef>
      <paramdef><parameter><optional>...</optional></parameter></paramdef>
     </funcprototype>
    </funcsynopsis>

    <para>
     <function>array_unshift</function> prepends passed elements to
     the front of the <parameter>array</parameter>. Note that the list
     of elements is prepended as a whole, so that the prepended
     elements stay in the same order.</para>

    <para>
     Returns the new number of elements in the
     <parameter>array</parameter>.</para>

    <para>
     <example>
      <title><function>array_unshift</function> example</title>
      <programlisting>
$queue = array("p1", "p3");
array_unshift($queue, "p4", "p5", "p6");
      </programlisting>
     </example>
     This would result in $queue having 5 elements: "p4", "p5", "p6",
     "p1", and "p3".</para>

    <para>
     See also <function>array_shift</function>,
     <function>array_push</function>, and
     <function>array_pop</function>.

    <note>
     <para>
      This function was added in PHP 4.0.</para> 
    </note></para>
   </refsect1>
  </refentry>

  <refentry id="function.array-values">
   <refnamediv>
    <refname>array_values</refname>
    <refpurpose>Return all the values of an array</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>array <function>array_values</function></funcdef>
     <paramdef>array <parameter>input</parameter></paramdef>
    </funcsynopsis>

    <para>
     <function>array_values</function> returns all the values from the
     <parameter>input</parameter> array.</para>

    <para>
     <example>
      <title><function>array_values</function> example</title>
      <programlisting>
$array = array("size" => "XL", "color" => "gold");
array_values($array);    // returns array("XL", "gold")
      </programlisting>
     </example>

     <note>
      <para>
      This function was added in PHP 4.0.</para>
     </note></para>
   </refsect1>
  </refentry>

  <refentry id="function.array-walk">
   <refnamediv>
    <refname>array_walk</refname>
    <refpurpose>
     Apply a user function to every member of an array.
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>int <function>array_walk</function></funcdef>
     <paramdef>array <parameter>arr</parameter></paramdef>
     <paramdef>string <parameter>func</parameter></paramdef>
     <paramdef>mixed <parameter>userdata</parameter></paramdef>
    </funcsynopsis>

    <simpara>
     Applies the function named by <parameter>func</parameter> to each
     element of
     <parameter>arr</parameter>. <parameter>func</parameter> will be
     passed array value as the first parameter and array key as the
     second parameter.  If <parameter>userdata</parameter> is
     supplied, it will be passed as the third parameter to the user
     function.

     If <parameter>func</parameter> requires more than two or three
     arguments, depending on <parameter>userdata</parameter>, a
     warning will be generated each time
     <function>array_walk</function> calls
     <parameter>func</parameter>. These warnings may be suppressed by
     prepending the '@' sign to the <function>array_walk</function>
     call, or by using <function>error_reporting</function>.</simpara>

    <note>
     <para>
      If <parameter>func</parameter> needs to be working with the
      actual values of the array, specify that the first parameter of
      <parameter>func</parameter> should be passed by reference. Then
      any changes made to those elements will be made in the array
      itself.
     </para>
    </note>

    <note>
     <para>
      Passing the key and userdata to <parameter>func</parameter> was added in 4.0.</para>
    </note>
    
    <para>
     <example>
      <title><function>array_walk</function> example</title>
      <programlisting>
$fruits = array("d"=>"lemon","a"=>"orange","b"=>"banana","c"=>"apple");

function test_alter( &$item1, $key, $prefix ) {
   $item1 = "$prefix: $item1";
}

function test_print( $item2, $key ) {
   echo "$key. $item2&lt;br&gt;\n";
}

array_walk( $fruits, 'test_print' );
array_walk( $fruits, 'test_alter', 'fruit' );
array_walk( $fruits, 'test_print' );
      </programlisting>
     </example></para>

    <simpara>
     See also <function>each</function> and <function>list</function>.</simpara>

   </refsect1>
  </refentry>

  <refentry id="function.arsort">
   <refnamediv>
    <refname>arsort</refname>
    <refpurpose>
     Sort an array in reverse order and maintain index association
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>void <function>arsort</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>
    <para>
     This function sorts an array such that array indices maintain
     their correlation with the array elements they are associated
     with.  This is used mainly when sorting associative arrays where
     the actual element order is significant.
     <example>
      <title><function>arsort</function> example</title>
      <programlisting>
$fruits = array("d"=>"lemon","a"=>"orange","b"=>"banana","c"=>"apple");
arsort($fruits);
for(reset($fruits); $key = key($fruits); next($fruits)) {
    echo "fruits[$key] = ".$fruits[$key]."\n";
}
</programlisting></example>
     This example would display:
     <computeroutput>
fruits[a] = orange
fruits[d] = lemon
fruits[b] = banana
fruits[c] = apple
</computeroutput>
     The fruits have been sorted in reverse alphabetical order, and
     the index associated with each element has been maintained.</para>
    <para>
     See also: <function>asort</function>, <function>rsort</function>,
     <function>ksort</function>, and <function>sort</function>.</para>
   </refsect1>
  </refentry>

  <refentry id="function.asort">
   <refnamediv>
    <refname>asort</refname>
    <refpurpose>Sort an array and maintain index association</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>void <function>asort</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>
    <para>
     This function sorts an array such that array indices maintain
     their correlation with the array elements they are associated
     with.  This is used mainly when sorting associative arrays where
     the actual element order is significant.
     <example>
      <title><function>asort</function> example</title>
      <programlisting>
$fruits = array("d"=>"lemon","a"=>"orange","b"=>"banana","c"=>"apple");
asort($fruits);
for(reset($fruits); $key = key($fruits); next($fruits)) {
    echo "fruits[$key] = ".$fruits[$key]."\n";
}
</programlisting></example>
     This example would display:
     <computeroutput>
fruits[c] = apple
fruits[b] = banana
fruits[d] = lemon
fruits[a] = orange
</computeroutput>
     The fruits have been sorted in alphabetical order, and the index
     associated with each element has been maintained.</para>
    <para>
     See also <function>arsort</function>, <function>rsort</function>,
     <function>ksort</function>, and <function>sort</function>.</para>
   </refsect1>
  </refentry>

  <refentry id="function.compact">
   <refnamediv>
    <refname>compact</refname>
    <refpurpose>
     Create array containing variables and their values
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>array <function>compact</function></funcdef>
     <paramdef><parameter>string varname | array
     varnames</parameter></paramdef>
     <paramdef><parameter><optional>...</optional></parameter></paramdef>
    </funcsynopsis>

    <para>
     <function>compact</function> takes a variable number of
     parameters. Each parameter can be either a string containing the
     name of the variable, or an array of variable names.  The array
     can contain other arrays of variable names inside it;
     <function>compact</function> handles it recursively.</para>

    <para>
     For each of these, <function>compact</function> looks for a
     variable with that name in the current symbol table and adds it
     to the output array such that the variable name becomes the key
     and the contents of the variable become the value for that key.
     In short, it does the opposite of <function>extract</function>.
     It returns the output array with all the variables added to it.</para>

    <para>
     <example>
      <title><function>compact</function> example</title>
      <programlisting>
$city = "San Francisco";
$state = "CA";
$event = "SIGGRAPH";

$location_vars = array("city", "state");

$result = compact("event", $location_vars);
      </programlisting>

      <para>
       After this, $result will be array("event" => "SIGGRAPH", "city"
       => "San Francisco", "state" => "CA").</para>
     </example></para>

    <para>
     See also <function>extract</function>.

    <note>
     <para>
      This function was added in PHP 4.0.</para>
    </note></para>
   </refsect1>
  </refentry>

  <refentry id="function.count">
   <refnamediv>
    <refname>count</refname>
    <refpurpose>count elements in a variable</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>int <function>count</function></funcdef>
     <paramdef>mixed <parameter>var</parameter></paramdef>
    </funcsynopsis>
    <para>
     Returns the number of elements in <parameter>var</parameter>,
     which is typically an array (since anything else will have one
     element).</para>
    <para>
     Returns 1 if the variable is not an array.</para>
    <para>
     Returns 0 if the variable is not set.
    <warning>
     <para>
      <function>count</function> may return 0 for a variable that
      isn't set, but it may also return 0 for a variable that has been
      initialized with an empty array. Use <function>isset</function>
      to test if a variable is set.
     </para>
    </warning></para>
    <para>
     See also:
     <function>sizeof</function>, <function>isset</function>, and
     <function>is_array</function>.</para>
   </refsect1>
  </refentry>

  <refentry id="function.current">
   <refnamediv>
    <refname>current</refname>
    <refpurpose>Return the current element in an array</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>mixed <function>current</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>
    <para>
     Every array has an internal pointer to its "current" element,
     which is initialized to the first element inserted into the
     array.</para>

    <para>
     The <function>current</function> function simply returns the
     array element that's currently being pointed by the internal
     pointer.  It does not move the pointer in any way.  If the
     internal pointer points beyond the end of the elements list,
     <function>current</function> returns false.

    <warning>
     <para> If the array contains empty elements (0 or "", the empty
     string) then this function will return false for these elements
     as well.  This makes it impossible to determine if you are really
     at the end of the list in such an array using
     <function>current</function>.  To properly traverse an array that
     may contain empty elements, use the <function>each</function>
     function.</para>
    </warning></para>

    <para>
     See also:
     <function>end</function>, <function>next</function>,
     <function>prev</function> and <function>reset</function>.</para>
   </refsect1>
  </refentry>


  <refentry id="function.each">
   <refnamediv>
    <refname>each</refname> 
    <refpurpose>
     Return the next key and value pair from an array
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>array <function>each</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>
    <para>
     Returns the current key and value pair from the array
     <parameter>array</parameter> and advances the array cursor. This
     pair is returned in a four-element array, with the keys
     <emphasis>0</emphasis>, <emphasis>1</emphasis>,
     <emphasis>key</emphasis>, and
     <emphasis>value</emphasis>. Elements <emphasis>0</emphasis> and
     <emphasis>key</emphasis> contain the key name of the array
     element, and <emphasis>1</emphasis> and
     <emphasis>value</emphasis> contain the data.</para>

    <para>
     If the internal pointer for the array points past the end of the
     array contents, <function>each</function> returns false.</para>
     
    <para>
     <example>
      <title><function>each</function> examples</title>
      <programlisting>
$foo = array ("bob", "fred", "jussi", "jouni", "egon", "marliese");
$bar = each( $foo );
      </programlisting>

      <para>
       <literal>$bar</literal> now contains the following key/value
       pairs:
       
       <itemizedlist spacing="compact">
        <listitem><simpara>0 => 0</simpara></listitem>
        <listitem><simpara>1 => 'bob'</simpara></listitem>
        <listitem><simpara>key => 0</simpara></listitem>
        <listitem><simpara>value => 'bob'</simpara></listitem>
       </itemizedlist>

       <programlisting>
$foo = array( "Robert" => "Bob", "Seppo" => "Sepi" );
$bar = each( $foo );
       </programlisting></para>

      <para>
       <literal>$bar</literal> now contains the following key/value
       pairs:

       <itemizedlist spacing="compact">
        <listitem><simpara>0 => 'Robert'</simpara></listitem>
        <listitem><simpara>1 => 'Bob'</simpara></listitem>
        <listitem><simpara>key => 'Robert'</simpara></listitem>
        <listitem><simpara>value => 'Bob'</simpara></listitem>
       </itemizedlist></para>

    </example></para>
      
    <para>
     <function>each</function> is typically used in conjunction with
     <function>list</function> to traverse an array; for instance,
     $HTTP_POST_VARS: 

     <example>
      <title>
       Traversing $HTTP_POST_VARS with <function>each</function>
      </title>
      <programlisting>
echo "Values submitted via POST method:&lt;br&gt;";
while (list($key, $val) = each($HTTP_POST_VARS)) {
   echo "$key => $val&lt;br&gt;";
}
      </programlisting>
     </example></para>

     <para>
      After <function>each</function> has executed, the array cursor
      will be left on the next element of the array, or on the last
      element if it hits the end of the array.</para>

    <para>
     See also <function>key</function>, <function>list</function>,
	 <function>current</function>, <function>reset</function>,
	 <function>next</function>, and <function>prev</function>.</para>

   </refsect1>
  </refentry>


  <refentry id="function.end">
   <refnamediv>
    <refname>end</refname>
    <refpurpose>
     Set the internal pointer of an array to its last element
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef><function>end</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>
    <para>
     <function>end</function> advances <parameter>array</parameter>'s
     internal pointer to the last element.</para>
    <para>
     See also:
     <function>current</function>, 
     <function>each</function>, 
     <function>end</function>,
     <function>next</function>, and 
     <function>reset</function>.</para>
   </refsect1>
  </refentry>

  <refentry id="function.extract">
   <refnamediv>
    <refname>extract</refname>
    <refpurpose>
     Import variables into the symbol table from an array
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>void <function>extract</function></funcdef>
     <paramdef>array <parameter>var_array</parameter></paramdef>
     <paramdef>int 
      <parameter><optional>extract_type</optional></parameter>
     </paramdef>
     <paramdef>string 
      <parameter><optional>prefix</optional></parameter>
     </paramdef>
    </funcsynopsis>
    <para>
     This function is used to import variables from an array into the
     current symbol table.  It takes associative array
     <parameter>var_array</parameter> and treats keys as variable
     names and values as variable values.  For each key/value pair it
     will create a variable in the current symbol table, subject to
     <parameter>extract_type</parameter> and
     <parameter>prefix</parameter> parameters.</para>
    <para>
     <function>extract</function> checks for colissions with existing
     variables.  The way collisions are treated is determined by
     <parameter>extract_type</parameter>. It can be one of the
     following values:
     <variablelist>
      <varlistentry>
       <term>EXTR_OVERWRITE</term>
       <listitem>
	<simpara>
	 If there is a collision, overwrite the existing variable.
	</simpara>
       </listitem>
      </varlistentry>
      <varlistentry>
       <term>EXTR_SKIP</term>
       <listitem>
	<simpara>
	 If there is a collision, don't overwrite the existing variable.
	</simpara>
       </listitem>
      </varlistentry>
      <varlistentry>
       <term>EXTR_PREFIX_SAME</term>
       <listitem>
	<simpara>If there is a collision, prefix the new variable with
	 <parameter>prefix</parameter>.
	</simpara>
       </listitem>
      </varlistentry>
      <varlistentry>
       <term>EXTR_PREFIX_ALL</term>
       <listitem>
	<simpara>
	 Prefix all variables with <parameter>prefix</parameter>.
	</simpara>
       </listitem>
      </varlistentry>
     </variablelist></para>
    <para>
     If <parameter>extract_type</parameter> is not specified, it is
     assumed to be EXTR_OVERWRITE.</para>
    <para>
     Note that <parameter>prefix</parameter> is only required if
     <parameter>extract_type</parameter> is EXTR_PREFIX_SAME or
     EXTR_PREFIX_ALL.</para>
    <para>
     <function>extract</function> checks each key to see if it
     constitues a valid variable name, and if it does only then does
     it proceed to import it.</para>
    <para>
     A possible use for extract is to import into symbol table
     variables contained in an associative array returned by
     <function>wddx_deserialize</function>.</para>
    <para>
     <example>
      <title>extract example</title>
      <programlisting>
&lt;?

/* Suppose that $var_array is an array returned from
   wddx_deserialize */
$size = "large";
$var_array = array("color" => "blue",
                   "size"  => "medium",
                   "shape" => "sphere");
extract($var_array, EXTR_PREFIX_SAME, "wddx");

print "$color, $size, $shape, $wddx_size\n";

?>
      </programlisting>
     </example></para>
	 
	<para>
	 The above example will produce:
	 <programlisting>
blue, large, sphere, medium
	 </programlisting></para>
	 
    <para>
     The $size wasn't overwritten, becaus we specified
     EXTR_PREFIX_SAME, which resulted in $wddx_size being created. 
     If EXTR_SKIP was specified, then $wddx_size wouldn't even have
     been created.  EXTR_OVERWRITE would have cause $size to have
     value "medium", and EXTR_PREFIX_ALL would result in new
     variables being named $wddx_color, $wddx_size, and $wddx_shape.</para>
   </refsect1>
  </refentry>

  <refentry id="function.in-array">
   <refnamediv>
    <refname>in_array</refname>
    <refpurpose>Return true if a value exists in an array</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>bool in_array</funcdef>
     <paramdef>mixed <parameter>needle</parameter></paramdef>
     <paramdef>array <parameter>haystack</parameter></paramdef>
    </funcsynopsis>

    <para>
     Searches <parameter>haystack</parameter> for
     <parameter>needle</parameter> and returns true if it is found in
     the array, false otherwise.</para>

    <para>
     <example>
      <title><function>in_array</function> example</title>
      <programlisting>
$os = array("Mac", "NT", "Irix", "Linux");
if (in_array("Irix", $os))
       print "Got Irix";
      </programlisting>
     </example>

    <note>
     <para>
      This function was added in PHP 4.0.</para> 
    </note></para>
   </refsect1>
  </refentry>

  <refentry id="function.key">
   <refnamediv>
    <refname>key</refname>
    <refpurpose>Fetch a key from an associative array</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>mixed <function>key</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>
    <para>
     <function>key</function> returns the index element of the
     current array position.</para>
    <para>
     See also:
     <function>current</function>,
     <function>next</function></para>
   </refsect1>
  </refentry>

  <refentry id="function.krsort">
   <refnamediv>
    <refname>krsort</refname>
    <refpurpose>Sort an array by key in reverse order</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>int <function>krsort</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>
    
    <para>
     Sorts an array by key in reverse order, maintaining key to data correlations. This
     is useful mainly for associative arrays.

    <example>
      <title><function>krsort</function> example</title>
      <programlisting>
$fruits = array("d"=>"lemon","a"=>"orange","b"=>"banana","c"=>"apple");
krsort($fruits);
for(reset($fruits); $key = key($fruits); next($fruits)) {
    echo "fruits[$key] = ".$fruits[$key]."\n";
}
</programlisting></example>
     This example would display:
     <computeroutput>
fruits[d] = lemon
fruits[c] = apple
fruits[b] = banana
fruits[a] = orange
</computeroutput></para>

    <simpara>
     See also <function>asort</function>, <function>arsort</function>, <function>ksort</function>
     <function>sort</function>, and <function>rsort</function>.</simpara>

   </refsect1>
  </refentry>



  <refentry id="function.ksort">
   <refnamediv>
    <refname>ksort</refname>
    <refpurpose>Sort an array by key</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>int <function>ksort</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>
    
    <para>
     Sorts an array by key, maintaining key to data correlations. This
     is useful mainly for associative arrays.

    <example>
      <title><function>ksort</function> example</title>
      <programlisting>
$fruits = array("d"=>"lemon","a"=>"orange","b"=>"banana","c"=>"apple");
ksort($fruits);
for(reset($fruits); $key = key($fruits); next($fruits)) {
    echo "fruits[$key] = ".$fruits[$key]."\n";
}
</programlisting></example>
     This example would display:
     <computeroutput>
fruits[a] = orange
fruits[b] = banana
fruits[c] = apple
fruits[d] = lemon
</computeroutput></para>

    <simpara>
     See also <function>asort</function>, <function>arsort</function>, 
     <function>sort</function>, and <function>rsort</function>.</simpara>

   </refsect1>
  </refentry>


  <refentry id="function.list">
   <refnamediv>
    <refname>list</refname>
    <refpurpose>
     Assign variables as if they were an array
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>void <function>list</function></funcdef>
     <varargs>
    </funcsynopsis>
    <para>
     Like <function>array</function>, this is not really a function,
     but a language construct.  <function>list</function> is used to
     assign a list of variables in one operation.

     <example>
      <title><function>list</function> example</title>
      <programlisting>
&lt;table>
 &lt;tr>
  &lt;th>Employee name&lt;/th>
  &lt;th>Salary&lt;/th>
 &lt;/tr>
&lt;?php

$result = mysql($conn, "SELECT id, name, salary FROM employees");
while (list($id, $name, $salary) = mysql_fetch_row($result)) {
    print(" &lt;tr>\n".
          "  &lt;td>&lt;a href=\"info.php3?id=$id\">$name&lt;/a>&lt;/td>\n".
          "  &lt;td>$salary&lt;/td>\n".
          " &lt;/tr>\n");
}

?>&lt;/table>
</programlisting></example></para>

    <para>
     See also: <function>each</function>, <function>array</function>.</para>
   </refsect1>
  </refentry>

  <refentry id="function.next">
   <refnamediv>
    <refname>next</refname>
    <refpurpose>
     Advance the internal array pointer of an array
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>mixed <function>next</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>
    <para>
     Returns the array element in the next place that's pointed by the
     internal array pointer, or false if there are no more elements.</para>
    <para>
     <function>next</function> behaves like
     <function>current</function>, with one difference.  It advances
     the internal array pointer one place forward before returning the
     element.  That means it returns the next array element and
     advances the internal array pointer by one.  If advancing the
     internal array pointer results in going beyond the end of the
     element list, <function>next</function> returns false.
     <warning>
      <para>
       If the array contains empty elements then this function will
       return false for these elements as well.  To properly traverse
       an array which may contain empty elements see the
       <function>each</function> function.
      </para>
    </warning></para>

    <para>
     See also:
     <function>current</function>, <function>end</function>
     <function>prev</function> and <function>reset</function></para>
   </refsect1>
  </refentry>

  <refentry id="function.pos">
   <refnamediv>
    <refname>pos</refname>
    <refpurpose>Get the current element from an array</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>mixed <function>pos</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>
    <simpara>
     This is an alias for <function>current</function>.</simpara>
    <para>
     See also:
     <function>end</function>, <function>next</function>,
     <function>prev</function> and <function>reset</function>.</para>
   </refsect1>
  </refentry>

  <refentry id="function.prev">
   <refnamediv>
    <refname>prev</refname>
    <refpurpose>Rewind the internal array pointer</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>mixed <function>prev</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>
    <para>
     Returns the array element in the previous place that's pointed by
     the internal array pointer, or false if there are no more
     elements.

    <warning>
     <para>
      If the array contains empty elements then this function will
      return false for these elements as well.  To properly traverse
      an array which may contain empty elements see the
      <function>each</function> function.
     </para>
    </warning></para>

    <para>  
     <function>prev</function> behaves just like
     <function>next</function>, except it rewinds the internal array
     pointer one place instead of advancing it.</para>

    <para>
     See also:
     <function>current</function>, <function>end</function>
     <function>next</function> and <function>reset</function></para>
   </refsect1>
  </refentry>

  <refentry id="function.range">
   <refnamediv>
    <refname>range</refname>
    <refpurpose>
     Create an array containing a range of integers
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>array <function>range</function></funcdef>
     <paramdef>int <parameter>low</parameter></paramdef>
     <paramdef>int <parameter>high</parameter></paramdef>
    </funcsynopsis>
    <para>
     <function>range</function> returns an array of integers from
     <parameter>low</parameter> to <parameter>high</parameter>,
     inclusive.</para>
    <para>
     See <function>shuffle</function> for an example of its use.</para>
   </refsect1>
  </refentry>

  <refentry id="function.reset">
   <refnamediv>
    <refname>reset</refname>
    <refpurpose>
     Set the internal pointer of an array to its first element
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>mixed <function>reset</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>
    <para>
     <function>reset</function> rewinds <parameter>array</parameter>'s
     internal pointer to the first element.</para>
    <para>
     <function>reset</function> returns the value of the first array
     element.</para>
    <para>
     See also: 
     <function>current</function>,
     <function>each</function>, 
     <function>next</function>,
     <function>prev</function>, and 
     <function>reset</function>.</para>
   </refsect1>
  </refentry>

  <refentry id="function.rsort">
   <refnamediv>
    <refname>rsort</refname>
    <refpurpose>Sort an array in reverse order</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>void <function>rsort</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>
    <para>
     This function sorts an array in reverse order (highest to lowest).
     <example>
      <title><function>rsort</function> example</title>
	<programlisting>
$fruits = array("lemon","orange","banana","apple");
rsort($fruits);
for (reset($fruits); list($key,$value) = each($fruits); ) {
    echo "fruits[$key] = ", $value, "\n";
}
      </programlisting>
     </example>

     This example would display:

     <computeroutput>
fruits[0] = orange
fruits[1] = lemon
fruits[2] = banana
fruits[3] = apple
     </computeroutput>

     The fruits have been sorted in reverse alphabetical order.</para>

    <para>
     See also:
     <function>arsort</function>, 
     <function>asort</function>,
     <function>ksort</function>, 
     <function>sort</function>, and
     <function>usort</function>.</para>
   </refsect1>
  </refentry>

  <refentry id="function.shuffle">
   <refnamediv>
    <refname>shuffle</refname>
    <refpurpose>Shuffle an array</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>void <function>shuffle</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>
    <para>
     This function shuffles (randomizes the order of the elements in)
     an array.
     <example>
      <title><function>shuffle</function> example</title>
	<programlisting>
$numbers = range(1,20);
srand(time());
shuffle($numbers);
while (list(,$number) = each($numbers)) {
    echo "$number ";
}
</programlisting></example></para>
    <para>
     See also <function>arsort</function>, <function>asort</function>,
     <function>ksort</function>, <function>rsort</function>,
     <function>sort</function> and <function>usort</function>.</para>
   </refsect1>
  </refentry>

  <refentry id="function.sizeof">
   <refnamediv>
    <refname>sizeof</refname>
    <refpurpose>Get the number of elements in an array</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>int <function>sizeof</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>
    <para>
     Returns the number of elements in the array.</para>
    <para>
     See also:
     <function>count</function></para>
   </refsect1>
  </refentry>

  <refentry id="function.sort">
   <refnamediv>
    <refname>sort</refname>
    <refpurpose>Sort an array</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>void <function>sort</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
    </funcsynopsis>
    <para>
     This function sorts an array.  Elements will be arranged from
     lowest to highest when this function has completed.
     <example>
      <title><function>sort</function> example</title>
	<programlisting>
$fruits = array("lemon","orange","banana","apple");
sort($fruits);
for(reset($fruits); $key = key($fruits); next($fruits)) {
    echo "fruits[$key] = ".$fruits[$key]."\n";
}
</programlisting></example>
     This example would display:
     <computeroutput>
fruits[0] = apple
fruits[1] = banana
fruits[2] = lemon
fruits[3] = orange
</computeroutput>
     The fruits have been sorted in alphabetical order.</para>
    <para>
     See also: 
     <function>arsort</function>, 
     <function>asort</function>,
     <function>ksort</function>, 
     <function>rsort</function>, and
     <function>usort</function>.</para>
   </refsect1>
  </refentry>

  <refentry id="function.uasort">
   <refnamediv>
    <refname>uasort</refname>
    <refpurpose>
     Sort an array with a user-defined comparison function and
     maintain index association
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>void <function>uasort</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
     <paramdef>function <parameter>cmp_function</parameter></paramdef>
    </funcsynopsis>
    <para>
     This function sorts an array such that array indices maintain
     their correlation with the array elements they are associated
     with.  This is used mainly when sorting associative arrays where
     the actual element order is significant.  The comparison function
     is user-defined.</para>
   </refsect1>
  </refentry>

  <refentry id="function.uksort">
   <refnamediv>
    <refname>uksort</refname>
    <refpurpose>
     Sort an array by keys using a user-defined comparison function
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>void <function>uksort</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
     <paramdef>function <parameter>cmp_function</parameter></paramdef>
    </funcsynopsis>
    <para>
     This function will sort the keys of an array using a
     user-supplied comparison function.  If the array you wish to sort
     needs to be sorted by some non-trivial criteria, you should use
     this function.

     <example>
      <title><function>uksort</function> example</title>
	<programlisting>
function mycompare($a, $b) {   
    if ($a == $b) return 0;
    return ($a > $b) ? -1 : 1;
}
$a = array(4 => "four", 3 => "three", 20 => "twenty", 10 => "ten");
uksort($a, mycompare);
while(list($key, $value) = each($a)) {
    echo "$key: $value\n";
}
</programlisting></example>

     This example would display:

     <computeroutput>
20: twenty
10: ten
4: four
3: three
     </computeroutput></para>

    <para>
     See also: 
     <function>arsort</function>, 
     <function>asort</function>,
     <function>uasort</function>, 
     <function>ksort</function>,
     <function>rsort</function>, and 
     <function>sort</function>.</para>

   </refsect1>
  </refentry>

  <refentry id="function.usort">
   <refnamediv>
    <refname>usort</refname>
    <refpurpose>
     Sort an array by values using a user-defined comparison function
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <funcsynopsis>
     <funcdef>void <function>usort</function></funcdef>
     <paramdef>array <parameter>array</parameter></paramdef>
     <paramdef>function <parameter>cmp_function</parameter></paramdef>
    </funcsynopsis>
    <para>
     This function will sort an array by its values using a
     user-supplied comparison function.  If the array you wish to sort
     needs to be sorted by some non-trivial criteria, you should use
     this function.</para>
    <para>
     The comparison function must return an integer less than, equal
     to, or greater than zero if the first argument is considered to
     be respectively less than, equal to, or greater than the
     second. If two members compare as equal, their order in the
     sorted array is undefined.
     <example>
      <title><function>usort</function> example</title>
	<programlisting>
function cmp($a,$b) {   
    if ($a == $b) return 0;
    return ($a > $b) ? -1 : 1;
}
$a = array(3,2,5,6,1);
usort($a, cmp);
while(list($key,$value) = each($a)) {
    echo "$key: $value\n";
}
</programlisting></example>
     This example would display:
     <computeroutput>
0: 6
1: 5
2: 3
3: 2
4: 1
</computeroutput>

    <note>
     <para>
      Obviously in this trivial case the <function>rsort</function>
      function would be more appropriate.
     </para>
    </note>

    <warning>
     <para>
      The underlying quicksort function in some C libraries (such as on
      Solaris systems) may cause PHP to crash if the comparison function
      does not return consistent values.
     </para>
    </warning></para>

    <para>
     See also:
      <function>arsort</function>, <function>asort</function>,
      <function>ksort</function>, <function>rsort</function> and
      <function>sort</function>.</para>

   </refsect1>
  </refentry>

 </reference>

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