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<HTML
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>usort</TITLE
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><H1
><A
NAME="function.usort"
>usort</A
></H1
><DIV
CLASS="refnamediv"
><A
NAME="AEN5872"
></A
><P
>    (PHP3 &#62;= 3.0.3, PHP4 )</P
>usort&nbsp;--&nbsp;
     Sort an array by values using a user-defined comparison function
    </DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN5875"
></A
><H2
>Description</H2
><DIV
CLASS="funcsynopsis"
><A
NAME="AEN5877"
></A
><P
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void <B
CLASS="function"
>usort</B
></CODE
> (array array, string cmp_function)</CODE
></P
><P
></P
></DIV
><P
>&#13;     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.
    </P
><P
>&#13;     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.
    </P
><P
>&#13;     <TABLE
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CLASS="EXAMPLE"
><TR
><TD
><DIV
CLASS="example"
><A
NAME="AEN5888"
></A
><P
><B
>Example 1. <B
CLASS="function"
>Usort()</B
> example</B
></P
><TABLE
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WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
>&#13;function cmp ($a, $b) {   
    if ($a == $b) return 0;
    return ($a &#62; $b) ? -1 : 1;
}

$a = array (3, 2, 5, 6, 1);

usort ($a, "cmp");

while (list ($key, $value) = each ($a)) {
    echo "$key: $value\n";
}
      </PRE
></TD
></TR
></TABLE
></DIV
></TD
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>
    </P
><P
>&#13;     This example would display:
    </P
><P
>&#13;     <DIV
CLASS="informalexample"
><A
NAME="AEN5894"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
>&#13;0: 6
1: 5
2: 3
3: 2
4: 1
      </PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
    </P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Note: </B
>
      Obviously in this trivial case the <A
HREF="function.rsort.html"
><B
CLASS="function"
>rsort()</B
></A
>
      function would be more appropriate.
     </P
></BLOCKQUOTE
></DIV
><P
>&#13;     <TABLE
WIDTH="100%"
BORDER="0"
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CLASS="EXAMPLE"
><TR
><TD
><DIV
CLASS="example"
><A
NAME="AEN5900"
></A
><P
><B
>Example 2. 
       <B
CLASS="function"
>Usort()</B
> example using multi-dimensional array
      </B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
>&#13;function cmp ($a, $b) {
    return strcmp($a["fruit"],$b["fruit"]);
} 

$fruits[0]["fruit"] = "lemons";
$fruits[1]["fruit"] = "apples";
$fruits[2]["fruit"] = "grapes";

usort($fruits, "cmp"); 

while (list ($key, $value) = each ($fruits)) {
    echo "\$fruits[$key]: " . $value["fruit"] . "\n";
}
      </PRE
></TD
></TR
></TABLE
></DIV
></TD
></TR
></TABLE
>
    </P
><P
>&#13;     When sorting a multi-dimensional array, $a and $b contain
     references to the first index of the array.
    </P
><P
>&#13;     This example would display:
    </P
><P
>&#13;     <DIV
CLASS="informalexample"
><A
NAME="AEN5907"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
>&#13;$fruits[0]: apples
$fruits[1]: grapes
$fruits[2]: lemons
      </PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
    </P
><P
>&#13;     <DIV
CLASS="warning"
><P
></P
><TABLE
CLASS="warning"
BORDER="1"
WIDTH="100%"
><TR
><TD
ALIGN="CENTER"
><B
>Warning</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
>&#13;       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.
      </P
></TD
></TR
></TABLE
></DIV
>
    </P
><P
>&#13;     See also: <A
HREF="function.uasort.html"
><B
CLASS="function"
>uasort()</B
></A
>, <A
HREF="function.uksort.html"
><B
CLASS="function"
>uksort()</B
></A
>, 
     <A
HREF="function.sort.html"
><B
CLASS="function"
>sort()</B
></A
>, <A
HREF="function.asort.html"
><B
CLASS="function"
>asort()</B
></A
>,
     <A
HREF="function.arsort.html"
><B
CLASS="function"
>arsort()</B
></A
>,<A
HREF="function.ksort.html"
><B
CLASS="function"
>ksort()</B
></A
>,
     <A
HREF="function.natsort.html"
><B
CLASS="function"
>natsort()</B
></A
>, and <A
HREF="function.rsort.html"
><B
CLASS="function"
>rsort()</B
></A
>.
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