Note: isset only takes on variables. Closes bug #20454

Also using var_dump() instead of print in examples.  Expanded examples a bit.


git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@104406 c90b9560-bf6c-de11-be94-00142212c4b1

reference/var/functions/isset.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="iso-8859-1"?>
-<!-- $Revision: 1.5 $ -->
+<!-- $Revision: 1.6 $ -->
 <!-- splitted from ./en/functions/var.xml, last change in rev 1.2 -->
   <refentry id="function.isset">
    <refnamediv>
@@ -28,22 +28,44 @@
      return &false; if testing a variable that has been set to &null;. Also
      note that a &null; byte (<literal>"\0"</literal>) is not equivalent to
      the PHP &null; constant.
+    </para>
+    <note>
+     <title>Warning</title>
+     <para>
+      <function>isset</function> only works with variables as passing anything
+      else will result in a parse error.
+     </para>
+    </note>
+    <para>
      <informalexample>
       <programlisting role="php">
 <![CDATA[
 <?php
-    $a = "test";
-    $b = "anothertest";
 
-    echo isset ($a); // TRUE
-    echo isset ($a, $b); //TRUE
+$var = '';
 
-    unset ($a);
-    echo isset ($a); // FALSE
-    echo isset ($a, $b); //FALSE
+// This will evaluate to &true; so the text will be printed.
+if (isset($var)) {
+    print "This var is set set so I will print.";
+}
+
+// In the next examples we'll use var_dump to output
+// the return value of isset().
+
+$a = "test";
+$b = "anothertest";
+
+var_dump( isset($a) );      // TRUE
+var_dump( isset ($a, $b) ); // TRUE
+
+unset ($a);
+
+var_dump( isset ($a) );     // FALSE
+var_dump( isset ($a, $b) ); // FALSE
 
 $foo = NULL;
-    print isset ($foo); // FALSE
+var_dump( isset ($foo) );   // FALSE
+
 ?>
 ]]>
       </programlisting>
@@ -55,12 +77,17 @@ $foo = NULL;
       <programlisting role="php">
 <![CDATA[
 <?php
-    $a = array ('test' => 1, 'hello' => null);
 
-    echo isset ($a['test']);  // TRUE
-    echo isset ($a['foo']);   // FALSE
-    echo isset ($a['hello']); // FALSE
-    echo array_key_exists('hello', $a); // TRUE
+$a = array ('test' => 1, 'hello' => NULL);
+
+var_dump( isset ($a['test']) );            // TRUE
+var_dump( isset ($a['foo']) );             // FALSE
+var_dump( isset ($a['hello']) );           // FALSE
+
+// The key 'hello' equals NULL so is considered unset
+// If you want to check for NULL key values then try: 
+var_dump( array_key_exists('hello', $a) ); // TRUE
+
 ?>
 ]]>
       </programlisting>