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php-manual-en-4.3.0-2mdk.noarch.rpm

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>isset</H1
><DIV
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><A
NAME="AEN94265"
></A
><P
>    (PHP 3, PHP 4 )</P
>isset&nbsp;--&nbsp;Determine whether a variable is set</DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN94268"
></A
><H2
>Description</H2
>bool <B
CLASS="methodname"
>isset</B
> ( mixed var [, mixed var [, ...]])<BR
></BR
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Note: </B
>
      <B
CLASS="function"
>isset()</B
> is a language construct.
     </P
></BLOCKQUOTE
></DIV
><P
>&#13;     Returns <TT
CLASS="constant"
><B
>TRUE</B
></TT
> if <TT
CLASS="parameter"
><I
>var</I
></TT
> exists; <TT
CLASS="constant"
><B
>FALSE</B
></TT
> otherwise.
    </P
><P
>&#13;     If a variable has been unset with <A
HREF="function.unset.html"
><B
CLASS="function"
>unset()</B
></A
>, it will no
     longer be <B
CLASS="function"
>isset()</B
>. <B
CLASS="function"
>isset()</B
> will
     return <TT
CLASS="constant"
><B
>FALSE</B
></TT
> if testing a variable that has been set to <TT
CLASS="constant"
><B
>NULL</B
></TT
>. Also
     note that a <TT
CLASS="constant"
><B
>NULL</B
></TT
> byte (<TT
CLASS="literal"
>"\0"</TT
>) is not equivalent to
     the PHP <TT
CLASS="constant"
><B
>NULL</B
></TT
> constant.
    </P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Warning: </B
>
      <B
CLASS="function"
>isset()</B
> only works with variables as passing anything
      else will result in a parse error.  For checking if 
      <A
HREF="language.constants.html"
>constants</A
> are set use the 
      <A
HREF="function.defined.html"
><B
CLASS="function"
>defined()</B
></A
> function.
     </P
></BLOCKQUOTE
></DIV
><P
>&#13;     <DIV
CLASS="informalexample"
><A
NAME="AEN94304"
></A
><P
></P
><TABLE
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><TD
><PRE
CLASS="php"
>&#60;?php

$var = '';

// This will evaluate to &#38;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

$foo = NULL;
var_dump( isset ($foo) );   // FALSE

?&#62;</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
    </P
><P
>&#13;     This also work for elements in arrays:
     <DIV
CLASS="informalexample"
><A
NAME="AEN94307"
></A
><P
></P
><TABLE
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><TD
><PRE
CLASS="php"
>&#60;?php

$a = array ('test' =&#62; 1, 'hello' =&#62; 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

?&#62;</PRE
></TD
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></P
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>
    </P
><P
>&#13;     See also <A
HREF="function.empty.html"
><B
CLASS="function"
>empty()</B
></A
>,
     <A
HREF="function.unset.html"
><B
CLASS="function"
>unset()</B
></A
>, <A
HREF="function.defined.html"
><B
CLASS="function"
>defined()</B
></A
>,
     <A
HREF="function.array-key-exists.html"
><B
CLASS="function"
>array_key_exists()</B
></A
> and the error control 
     <A
HREF="language.operators.errorcontrol.html"
>@</A
>
     operator.
    </P
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