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Adding zak's note
git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@48031 c90b9560-bf6c-de11-be94-00142212c4b1
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@ -810,13 +810,18 @@ show_var($proteins)
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</simpara>
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<para>
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If a variable has been unset with <function>unset</function>,
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it will no longer be <function>isset</function>.
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it will no longer be <function>isset</function>. <function>isset</function>
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will return <literal>FALSE</literal> if testing a variable that has been
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set to <literal>NULL</literal>. Also note that a null byte (<literal>"\0"</literal>)
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is not equivalent to the PHP <literal>NULL</literal> constant.
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<informalexample>
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<programlisting role="php">
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$a = "test";
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echo isset ($a); // true
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echo isset ($a); // TRUE
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unset ($a);
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echo isset ($a); // false
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echo isset ($a); // FALSE
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$foo = NULL;
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print isset ($foo); // FALSE
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</programlisting>
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</informalexample>
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</para>
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