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>function_exists</H1
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><P
>    (PHP 3&#62;= 3.0.7, PHP 4 )</P
>function_exists&nbsp;--&nbsp;
     Return <TT
CLASS="constant"
><B
>TRUE</B
></TT
> if the given function has been defined
    </DIV
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><H2
>Description</H2
>bool <B
CLASS="methodname"
>function_exists</B
> ( string function_name)<BR
></BR
><P
>&#13;     Checks the list of defined functions, both built-in (internal) and
     user-defined, for <TT
CLASS="parameter"
><I
>function_name</I
></TT
>. Returns <TT
CLASS="constant"
><B
>TRUE</B
></TT
> on success or <TT
CLASS="constant"
><B
>FALSE</B
></TT
> on failure.
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><PRE
CLASS="php"
>if (function_exists('imap_open')) {
    echo "IMAP functions are available.&#60;br&#62;\n";
} else {
    echo "IMAP functions are not available.&#60;br&#62;\n";
}</PRE
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>
     Note that a function name may exist even if the function itself
     is unusable due to configuration or compiling options (with the 
     <A
HREF="ref.image.html"
>image</A
> functions being an example).  
     Also note that <B
CLASS="function"
>function_exists()</B
> will return 
     <TT
CLASS="constant"
><B
>FALSE</B
></TT
> for constructs, such as <A
HREF="function.include-once.html"
><B
CLASS="function"
>include_once()</B
></A
> 
     and <A
HREF="function.echo.html"
><B
CLASS="function"
>echo()</B
></A
>.
    </P
><P
>&#13;     See also <A
HREF="function.method-exists.html"
><B
CLASS="function"
>method_exists()</B
></A
> and 
     <A
HREF="function.get-defined-functions.html"
><B
CLASS="function"
>get_defined_functions()</B
></A
>.
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