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

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><H1
><A
NAME="function.debug-zval-dump"
></A
>debug_zval_dump</H1
><DIV
CLASS="refnamediv"
><A
NAME="AEN236068"
></A
><P
>    (PHP 4 &#62;= 4.2.0, PHP 5)</P
>debug_zval_dump&nbsp;--&nbsp;Dumps a string representation of an internal zend value to output</DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN236071"
></A
><H2
>说明</H2
>void <B
CLASS="methodname"
>debug_zval_dump</B
> ( mixed variable )<BR
></BR
><P
>&#13;   Dumps a string representation of an internal zend value to output.
  </P
></DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN236080"
></A
><H2
>参数</H2
><P
>&#13;   <P
></P
><DIV
CLASS="variablelist"
><DL
><DT
><CODE
CLASS="parameter"
>variable</CODE
></DT
><DD
><P
>&#13;       The variable being evaluated.
      </P
></DD
></DL
></DIV
>
  </P
></DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN236089"
></A
><H2
>返回值</H2
><P
>&#13;   无返回值。
  </P
></DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN236092"
></A
><H2
>范例</H2
><P
>&#13;   <TABLE
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
CLASS="EXAMPLE"
><TR
><TD
><DIV
CLASS="example"
><A
NAME="AEN236095"
></A
><P
><B
>例 1. <B
CLASS="function"
>debug_zval_dump()</B
> example</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><code><font color="#000000">
<font color="#0000BB">&lt;?php<br />$var1 </font><font color="#007700">= </font><font color="#DD0000">'Hello World'</font><font color="#007700">;<br /></font><font color="#0000BB">$var2 </font><font color="#007700">= </font><font color="#DD0000">''</font><font color="#007700">;<br /><br /></font><font color="#0000BB">$var2 </font><font color="#007700">=&amp; </font><font color="#0000BB">$var1</font><font color="#007700">;<br /><br /></font><font color="#0000BB">debug_zval_dump</font><font color="#007700">(&amp;</font><font color="#0000BB">$var1</font><font color="#007700">);<br /></font><font color="#0000BB">?&gt;</font>
</font>
</code></TD
></TR
></TABLE
><P
>上例将输出：</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><PRE
CLASS="screen"
>string(11) "Hello World" refcount(3)</PRE
></TD
></TR
></TABLE
></DIV
></TD
></TR
></TABLE
>
  </P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Beware the <TT
CLASS="literal"
>refcount</TT
>: </B
>
    The <TT
CLASS="literal"
>refcount</TT
> value returned by this function is
    non-obvious in certain circumstances. For example, a developer might
    expect the above example to indicate a <TT
CLASS="literal"
>refcount</TT
> of
    <TT
CLASS="literal"
>2</TT
>. The third reference is created when actually
    calling <B
CLASS="function"
>debug_zval_dump()</B
>.
   </P
><P
>&#13;    This behavior is further compounded when a variable is not passed to
    <B
CLASS="function"
>debug_zval_dump()</B
> by reference. To illustrate, consider
    a slightly modified version of the above example:
   </P
><P
>&#13;    <TABLE
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
CLASS="EXAMPLE"
><TR
><TD
><DIV
CLASS="example"
><A
NAME="AEN236112"
></A
><P
><B
>例 2. </B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><code><font color="#000000">
<font color="#0000BB">&lt;?php<br />$var1 </font><font color="#007700">= </font><font color="#DD0000">'Hello World'</font><font color="#007700">;<br /></font><font color="#0000BB">$var2 </font><font color="#007700">= </font><font color="#DD0000">''</font><font color="#007700">;<br /><br /></font><font color="#0000BB">$var2 </font><font color="#007700">=&amp; </font><font color="#0000BB">$var1</font><font color="#007700">;<br /><br /></font><font color="#0000BB">debug_zval_dump</font><font color="#007700">(</font><font color="#0000BB">$var1</font><font color="#007700">); </font><font color="#FF8000">// not passed by reference, this time<br /></font><font color="#0000BB">?&gt;</font>
</font>
</code></TD
></TR
></TABLE
><P
>上例将输出：</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><PRE
CLASS="screen"
>string(11) "Hello World" refcount(1)</PRE
></TD
></TR
></TABLE
></DIV
></TD
></TR
></TABLE
>
   </P
><P
>&#13;    Why <TT
CLASS="literal"
>refcount(1)</TT
>? Because a copy of <TT
CLASS="literal"
>$var1</TT
> is
    being made, when the function is called.
   </P
><P
>&#13;    This function becomes even <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>more</I
></SPAN
> confusing when a
    variable with a <TT
CLASS="literal"
>refcount</TT
> of <TT
CLASS="literal"
>1</TT
> is
    passed (by copy/value):
   </P
><P
>&#13;    <TABLE
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
CLASS="EXAMPLE"
><TR
><TD
><DIV
CLASS="example"
><A
NAME="AEN236125"
></A
><P
><B
>例 3. </B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><code><font color="#000000">
<font color="#0000BB">&lt;?php<br />$var1 </font><font color="#007700">= </font><font color="#DD0000">'Hello World'</font><font color="#007700">;<br /><br /></font><font color="#0000BB">debug_zval_dump</font><font color="#007700">(</font><font color="#0000BB">$var1</font><font color="#007700">);<br /></font><font color="#0000BB">?&gt;</font>
</font>
</code></TD
></TR
></TABLE
><P
>上例将输出：</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><PRE
CLASS="screen"
>string(11) "Hello World" refcount(2)</PRE
></TD
></TR
></TABLE
></DIV
></TD
></TR
></TABLE
>
   </P
><P
>&#13;    A <TT
CLASS="literal"
>refcount</TT
> of <TT
CLASS="literal"
>2</TT
>, here, is extremely
    non-obvious. Especially considering the above examples. So what's
    happening?
   </P
><P
>&#13;    When a variable has a single reference (as did <TT
CLASS="literal"
>$var1</TT
>
    before it was used as an argument to <B
CLASS="function"
>debug_zval_dump()</B
>),
    PHP's engine optimizes the manner in which it is passed to a function.
    Internally, PHP treats <TT
CLASS="literal"
>$var1</TT
> like a reference (in that
    the <TT
CLASS="literal"
>refcount</TT
> is increased for the scope of this
    function), with the caveat that <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>if</I
></SPAN
> the passed reference
    happens to be written to, a copy is made, but only at the moment of
    writing. This is known as "copy on write."
   </P
><P
>&#13;    So, if <B
CLASS="function"
>debug_zval_dump()</B
> happened to write to its sole
    parameter (and it doesn't), then a copy would be made. Until then, the
    parameter remains a reference, causing the <TT
CLASS="literal"
>refcount</TT
> to
    be incremented to <TT
CLASS="literal"
>2</TT
> for the scope of the function call.
   </P
></BLOCKQUOTE
></DIV
></DIV
><DIV
CLASS="refsect1"
><A
NAME="AEN236143"
></A
><H2
>参见</H2
><P
>&#13;   <P
></P
><TABLE
BORDER="0"
><TBODY
><TR
><TD
><A
HREF="function.var-dump.html"
><B
CLASS="function"
>var_dump()</B
></A
></TD
></TR
><TR
><TD
><A
HREF="function.debug-backtrace.html"
><B
CLASS="function"
>debug_backtrace()</B
></A
></TD
></TR
><TR
><TD
><A
HREF="language.references.html"
>References Explained</A
></TD
></TR
><TR
><TD
><A
HREF="http://www.zend.com/zend/art/ref-count.php"
TARGET="_top"
>Reference Counting and Aliasing (by Andi Gutmans)</A
></TD
></TR
><TR
><TD
><A
HREF="http://derickrethans.nl/php_references_article.php"
TARGET="_top"
>References Explained (by Derick Rethans)</A
></TD
></TR
></TBODY
></TABLE
><P
></P
>
  </P
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