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php-manual-zh-5.2.4-1mdv2008.1.noarch.rpm

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><H1
><A
NAME="function.eval"
></A
>eval</H1
><DIV
CLASS="refnamediv"
><A
NAME="AEN125342"
></A
><P
>    (PHP 3, PHP 4, PHP 5)</P
>eval&nbsp;--&nbsp;Evaluate a string as PHP code</DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN125345"
></A
><H2
>说明</H2
>mixed <B
CLASS="methodname"
>eval</B
> ( string code_str )<BR
></BR
><P
>&#13;   Evaluates the string given in <CODE
CLASS="parameter"
>code_str</CODE
> as PHP code.
   Among other things, this can be useful for storing code in a database text
   field for later execution. 
  </P
><P
>&#13;   There are some factors to keep in mind when using
   <B
CLASS="function"
>eval()</B
>. Remember that the string passed must be valid
   PHP code, including things like terminating statements with a semicolon so
   the parser doesn't die on the line after the <B
CLASS="function"
>eval()</B
>,
   and properly escaping things in <CODE
CLASS="parameter"
>code_str</CODE
>. To mix
   HTML output and PHP code you can use a closing PHP tag to leave PHP mode.
  </P
><P
>&#13;   Also remember that variables given values under <B
CLASS="function"
>eval()</B
>
   will retain these values in the main script afterwards.
  </P
></DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN125361"
></A
><H2
>参数</H2
><P
>&#13;   <P
></P
><DIV
CLASS="variablelist"
><DL
><DT
><CODE
CLASS="parameter"
>code_str</CODE
></DT
><DD
><P
>&#13;       The code string to be evaluated.
       <CODE
CLASS="parameter"
>code_str</CODE
> does not have to contain <A
HREF="language.basic-syntax.html#language.basic-syntax.phpmode"
>PHP Opening tags</A
>.
      </P
><P
>&#13;       A <TT
CLASS="literal"
>return</TT
> statement will immediately terminate the
       evaluation of the string . 
      </P
></DD
></DL
></DIV
>
  </P
></DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN125374"
></A
><H2
>返回值</H2
><P
>&#13;   As of PHP 4, <B
CLASS="function"
>eval()</B
> returns <TT
CLASS="constant"
><B
>NULL</B
></TT
> unless 
   <TT
CLASS="literal"
>return</TT
> is called in the evaluated code, in which case
   the value passed to <TT
CLASS="literal"
>return</TT
> is returned. In case of a
   parse error in the evaluated code, <B
CLASS="function"
>eval()</B
> returns 
   <TT
CLASS="constant"
><B
>FALSE</B
></TT
>.
  </P
><P
>&#13;   In PHP 3, <B
CLASS="function"
>eval()</B
> does not return a value.
  </P
></DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN125385"
></A
><H2
>范例</H2
><P
>&#13;   <TABLE
WIDTH="100%"
BORDER="0"
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CELLSPACING="0"
CLASS="EXAMPLE"
><TR
><TD
><DIV
CLASS="example"
><A
NAME="AEN125388"
></A
><P
><B
>例 1. <B
CLASS="function"
>eval()</B
> example - simple text merge</B
></P
><TABLE
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CELLPADDING="5"
><TR
><TD
><code><font color="#000000">
<font color="#0000BB">&lt;?php<br />$string </font><font color="#007700">= </font><font color="#DD0000">'cup'</font><font color="#007700">;<br /></font><font color="#0000BB">$name </font><font color="#007700">= </font><font color="#DD0000">'coffee'</font><font color="#007700">;<br /></font><font color="#0000BB">$str </font><font color="#007700">= </font><font color="#DD0000">'This is a $string with my $name in it.'</font><font color="#007700">;<br />echo </font><font color="#0000BB">$str</font><font color="#007700">. </font><font color="#DD0000">"\n"</font><font color="#007700">;<br />eval(</font><font color="#DD0000">"</font><font color="#007700">\$</font><font color="#DD0000">str = </font><font color="#007700">\"</font><font color="#DD0000">$str</font><font color="#007700">\"</font><font color="#DD0000">;"</font><font color="#007700">);<br />echo </font><font color="#0000BB">$str</font><font color="#007700">. </font><font color="#DD0000">"\n"</font><font color="#007700">;<br /></font><font color="#0000BB">?&gt;</font>
</font>
</code></TD
></TR
></TABLE
><P
>上例将输出：</P
><TABLE
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><TD
><PRE
CLASS="screen"
>This is a $string with my $name in it.
This is a cup with my coffee in it.</PRE
></TD
></TR
></TABLE
></DIV
></TD
></TR
></TABLE
>
  </P
></DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN125394"
></A
><H2
>注释</H2
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>注意: </B
>由于这是一个语言结构而非函数，因此它无法被<A
HREF="functions.variable-functions.html"
>变量函数</A
>调用。</P
></BLOCKQUOTE
></DIV
><DIV
CLASS="tip"
><BLOCKQUOTE
CLASS="tip"
><P
><B
>提示: </B
>为了防止程序直接将结果输出到浏览器，可以使用<A
HREF="ref.outcontrol.html"
>输出控制函数</A
>来捕获此函数的输出，并把它们保存到一个例如
<A
HREF="language.types.string.html"
><B
CLASS="type"
>string</B
></A
> 类型的变量中。</P
></BLOCKQUOTE
></DIV
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>注意: </B
>
    In case of a fatal error in the evaluated code, the whole script exits.
   </P
></BLOCKQUOTE
></DIV
></DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN125405"
></A
><H2
>参见</H2
><P
>&#13;   <P
></P
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