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>defined</H1
><DIV
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><A
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></A
><P
> (PHP 3, PHP 4, PHP 5)</P
>defined -- Checks whether a given named constant exists</DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN125282"
></A
><H2
>说明</H2
>bool <B
CLASS="methodname"
>defined</B
> ( string name )<BR
></BR
><P
> Checks whether the given constant exists and is defined.
</P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>注意: </B
>
If you want to see if a variable exists, use <A
HREF="function.isset.html"
><B
CLASS="function"
>isset()</B
></A
>
as <B
CLASS="function"
>defined()</B
> only applies to <A
HREF="language.constants.html"
>constants</A
>. If you want to see if a
function exists, use <A
HREF="function.function-exists.html"
><B
CLASS="function"
>function_exists()</B
></A
>.
</P
></BLOCKQUOTE
></DIV
></DIV
><DIV
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><A
NAME="AEN125297"
></A
><H2
>参数</H2
><P
> <P
></P
><DIV
CLASS="variablelist"
><DL
><DT
><CODE
CLASS="parameter"
>name</CODE
></DT
><DD
><P
> The constant name.
</P
></DD
></DL
></DIV
>
</P
></DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN125306"
></A
><H2
>返回值</H2
><P
> Returns <TT
CLASS="constant"
><B
>TRUE</B
></TT
> if the named constant given by <CODE
CLASS="parameter"
>name</CODE
>
has been defined, <TT
CLASS="constant"
><B
>FALSE</B
></TT
> otherwise.
</P
></DIV
><DIV
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><A
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></A
><H2
>范例</H2
><P
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><P
><B
>例 1. Checking Constants</B
></P
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><code><font color="#000000">
<font color="#0000BB"><?php<br /></font><font color="#FF8000">/* Note the use of quotes, this is important. This example is checking<br /> * if the string 'CONSTANT' is the name of a constant named CONSTANT */<br /></font><font color="#007700">if (</font><font color="#0000BB">defined</font><font color="#007700">(</font><font color="#DD0000">'CONSTANT'</font><font color="#007700">)) {<br /> echo </font><font color="#0000BB">CONSTANT</font><font color="#007700">;<br />}<br /></font><font color="#0000BB">?></font>
</font>
</code></TD
></TR
></TABLE
></DIV
></TD
></TR
></TABLE
>
</P
></DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN125318"
></A
><H2
>参见</H2
><P
> <P
></P
><TABLE
BORDER="0"
><TBODY
><TR
><TD
><A
HREF="function.define.html"
><B
CLASS="function"
>define()</B
></A
></TD
></TR
><TR
><TD
><A
HREF="function.constant.html"
><B
CLASS="function"
>constant()</B
></A
></TD
></TR
><TR
><TD
><A
HREF="function.get-defined-constants.html"
><B
CLASS="function"
>get_defined_constants()</B
></A
></TD
></TR
><TR
><TD
><A
HREF="function.function-exists.html"
><B
CLASS="function"
>function_exists()</B
></A
></TD
></TR
><TR
><TD
>The section on <A
HREF="language.constants.html"
>Constants</A
></TD
></TR
></TBODY
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><P
></P
>
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