如何判定PHP运算符优先级别_PHP教程

学习php时，你可能会遇到php运算符优先级问题，这里将介绍php运算符优先级问题的解决方法，在这里拿出来和大家分享一下。php支持一个错误控制运算符：@。当将其放置在一个php表达式之前，该表达式可能产生的任何错误信息都被忽略掉。如果激活了track_errors特性，表达式所产生的任何错误信息都被存放在变量$php_errormsg中。此变量在每次出错时都会被覆盖，所以如果想用它的话就要尽早检查。

<OL class=dp-xml><LI class=alt><SPAN><STRONG><FONT color=#006699><SPAN class=tag><?</SPAN><SPAN class=tag-name>php</SPAN></FONT></STRONG><SPAN> </SPAN></SPAN><LI class=""><SPAN>$</SPAN><SPAN class=attribute><FONT color=#ff0000>my_file</FONT></SPAN><SPAN>=@file('non_existent_file')or  </SPAN></SPAN><LI class=alt><SPAN>die("Failedopeningfile:errorwas'$php_errormsg'");  </SPAN><LI class=""><SPAN>$</SPAN><SPAN class=attribute><FONT color=#ff0000>value</FONT></SPAN><SPAN>=@$cache[$key];  </SPAN></SPAN><LI class=alt><SPAN></SPAN><SPAN class=tag><STRONG><FONT color=#006699>?></FONT></STRONG></SPAN><SPAN> </SPAN></SPAN></LI></OL>

<OL class=dp-xml><LI class=alt><SPAN><STRONG><FONT color=#006699><SPAN class=tag><?</SPAN><SPAN class=tag-name>php</SPAN></FONT></STRONG><SPAN> </SPAN></SPAN><LI class=""><SPAN>$</SPAN><SPAN class=attribute><FONT color=#ff0000>output</FONT></SPAN><SPAN>=`ls-al`;  </SPAN></SPAN><LI class=alt><SPAN>echo"</SPAN><STRONG><FONT color=#006699><SPAN class=tag><</SPAN><SPAN class=tag-name>pre</SPAN><SPAN class=tag>></SPAN></FONT></STRONG><SPAN>$output</SPAN><STRONG><FONT color=#006699><SPAN class=tag></</SPAN><SPAN class=tag-name>pre</SPAN><SPAN class=tag>></SPAN></FONT></STRONG><SPAN>";  </SPAN></SPAN><LI class=""><SPAN></SPAN><SPAN class=tag><STRONG><FONT color=#006699>?></FONT></STRONG></SPAN><SPAN> </SPAN></SPAN></LI></OL>

注:反引号运算符在激活了安全模式或者关闭了shell_exec()时是无效的。

加一／减一运算符：
++$a前加$a的值加一，然后返回$a。
$a++后加返回$a，然后将$a的值加一。
--$a前减$a的值减一，然后返回$a。
$a--后减返回$a，然后将$a的值减一。

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这个跟c语言的自加，自减一样举个简单的例子加深一下

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