goto.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->

<sect1 xml:id="control-structures.goto" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <title>goto</title>
 <?phpdoc print-version-for="goto"?>
 <para>
  <mediaobject>
   <alt>What's the worse thing that could happen if you use goto?</alt>
   <imageobject>
    <imagedata fileref="en/language/figures/xkcd-goto.png" format="PNG"/>
   </imageobject>
   <caption>
    <simpara>
     Image courtesy of <link xlink:href="&url.xkcd;292">xkcd</link>
    </simpara>
   </caption>
  </mediaobject>
 </para>
 <para>
  The <literal>goto</literal> operator can be used to jump to another
  section in the program.  The target point is specified by a <emphasis>case-sensitive</emphasis> label
  followed by a colon, and the instruction is given as
  <literal>goto</literal> followed by the desired target label.  This
  is not a full unrestricted <literal>goto</literal>.  The target
  label must be within the same file and context, meaning that you cannot jump
  out of a function or method, nor can you jump into one.  You also
  cannot jump into any sort of loop or switch structure.  You may jump
  out of these, and a common use is to use a <literal>goto</literal>
  in place of a multi-level <literal>break</literal>.
 </para>
 <para>
  <example>
   <title><literal>goto</literal> example</title>
   <programlisting role="php">
<![CDATA[
<?php

goto a;
echo 'Foo';

a:
echo 'Bar';

?>
]]>
   </programlisting>
   &example.outputs;
   <screen>
<![CDATA[
Bar
]]>
   </screen>
  </example>
 </para>
 <para>
  <example>
   <title><literal>goto</literal> loop example</title>
   <programlisting role="php">
<![CDATA[
<?php

for ($i = 0, $j = 50; $i < 100; $i++) {
    while ($j--) {
        if ($j == 17) {
            goto end;
        }
    }
}
echo "i = $i";
end:
echo 'j hit 17';

?>
]]>
   </programlisting>
   &example.outputs;
   <screen>
<![CDATA[
j hit 17
]]>
   </screen>
  </example>
 </para>
 <para>
  <example>
   <title>This will not work</title>
   <programlisting role="php">
<![CDATA[
<?php

goto loop;
for ($i = 0, $j = 50; $i < 100; $i++) {
    while ($j--) {
        loop:
    }
}
echo "$i = $i";

?>
]]>
   </programlisting>
   &example.outputs;
   <screen>
<![CDATA[
Fatal error: 'goto' into loop or switch statement is disallowed in
script on line 2
]]>
   </screen>
  </example>
 </para>

</sect1>

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