异常处理try-catch-finally_PHP教程

<?<span>php
</span><span>/*</span><span>*
finally块是个很好的设计，其中的return语句能覆盖其他块中的return语句，并处理try catch抛出的异常
无需try-catch嵌套来处理子try-catch抛出的异常
这个跟java的一样，c#是在finally块中存在return语句会抛出compile time error（编译时错误）
</span><span>*/</span>

<span>function</span><span> asdf()
{
    </span><span>try</span><span> {
        </span><span>throw</span> <span>new</span> <span>Exception</span>('error'<span>);
    }
    </span><span>catch</span>(<span>Exception</span> <span>$e</span><span>) {
        </span><span>echo</span> "An error occurred"<span>;
        </span><span>throw</span> <span>$e</span><span>;
    }
    finally {
                </span><span>//</span><span>This overrides the exception as if it were never thrown</span>
        <span>return</span> "\nException erased"<span>;
    }
}

</span><span>try</span><span> {
    </span><span>echo</span><span> asdf();
}
</span><span>catch</span>(<span>Exception</span> <span>$e</span><span>) {
    </span><span>echo</span> "\nResult: " . <span>$e</span>-><span>getMessage();
}

</span><span>/*</span><span>
 The output from above will look like this:

     An error occurred
     Exception erased

 Without the return statement in the finally block it would look like this:

     An error occurred
     Result: error
</span><span>*/</span>

<?<span>php
</span><span>/*</span><span>*
有个相悖的行为在PHP 5.5.3's finally 和 return statements：
在一个方法中，try块单返回一个变量，finally块修改这个变量，返回的是finally修改过的，
但当try块返回的变量参与运算（evaluated in-line），会忽略finally块对这个变量的修改
（不知道原因...）
</span><span>*/</span>
<span>function</span><span> returnVariable(){
 </span><span>$foo</span> = 1<span>;
 </span><span>try</span><span>{
 </span><span>return</span> <span>$foo</span><span>;
 } finally {
 </span><span>$foo</span>++<span>;
 }
 }

 </span><span>function</span><span> returnVariablePlusZero(){
 </span><span>$foo</span> = 1<span>;
 </span><span>try</span><span>{
 </span><span>return</span> <span>$foo</span>+0<span>;
 } finally {
 </span><span>$foo</span>++<span>;
 }
 }

 </span><span>$test1</span> = returnVariable(); <span>//</span><span> returns 2, not the correct value of 1.</span>
 <span>$test2</span> = returnVariablePlusZero(); <span>//</span><span> returns correct value of 1, but inconsistent with $test1.</span>

<?<span>php
</span><span>/*</span><span>*
小例子 验证变量
check if the name contains only letters, and does not contain the word name
</span><span>*/</span>

<span>$name</span> = "Name"<span>;
</span><span>try</span><span>
{
        </span><span>try</span><span>
        {
                </span><span>//</span><span>preg_match() 返回 pattern  的匹配次数。 它的值将是0次（不匹配）或1次，因为 preg_match() 在第一次匹配后 将会停止搜索。 preg_match_all() 不同于此，它会一直搜索 subject  直到到达结尾。 如果发生错误 preg_match() 返回 FALSE 。</span>
                <span>if</span>(<span>preg_match</span>('/[^a-z]/i', <span>$name</span><span>))
                {
                        </span><span>throw</span> <span>new</span> <span>Exception</span>("<span>$name</span> contains character other than a-z A-Z"<span>);
                }
                </span><span>if</span>(<span>strpos</span>(<span>strtolower</span>(<span>$name</span>), 'name') !== <span>false</span><span>)
                {
                        </span><span>throw</span> <span>new</span> <span>Exception</span>("<span>$name</span> contains the word name"<span>);
                }
                </span><span>echo</span> "The Name is valid"<span>;
        }
        </span><span>catch</span> (<span>exception</span> <span>$e</span><span>)
        {
                </span><span>throw</span> <span>new</span> <span>Exception</span>("insert name again", 0, <span>$e</span><span>);
        }
}

</span><span>catch</span> (<span>exception</span> <span>$e</span><span>)
{
        </span><span>if</span>(<span>$e</span>-><span>getPrevious())
        {
                </span><span>echo</span> "The Previous Exception is: " . <span>$e</span>->getPrevious()->getMessage() . "<br/>"<span>;
        }
        </span><span>echo</span> "The Exception is: " . <span>$e</span>->getMessage() . "<br/>"<span>;
}</span>

<?<span>php
</span><span>/*</span><span>
When catching an exception inside a namespace it is important that you escape to the global space:
如何逃离出命名空间
</span><span>*/</span><span>

 namespace SomeNamespace;

 </span><span>class</span><span> SomeClass {

  </span><span>function</span><span> SomeFunction() {
   </span><span>try</span><span> {
    </span><span>throw</span> <span>new</span> <span>Exception</span>('Some Error Message'<span>);
   } </span><span>catch</span> (\<span>Exception</span> <span>$e</span><span>) {
    </span><span>var_dump</span>(<span>$e</span>-><span>getMessage());
   }
  }

 }

</span><span>//</span><span>报错：
//Fatal error: Class 'SomeNamespace\Exception' not found in C:\xampp\htdocs\tonglei\index.php on line 8</span>

<?<span>php

</span><span>//</span><span>下面的写法会报T_THROW Syntax Error.</span>
someFunction() OR <span>throw</span> <span>new</span> <span>Exception</span><span>();

</span><span>//</span><span>这种写法可以用下面这个正确的形式</span>
<span>function</span> throwException(<span>$message</span> = <span>null</span>,<span>$code</span> = <span>null</span><span>) {
    </span><span>throw</span> <span>new</span> <span>Exception</span>(<span>$message</span>,<span>$code</span><span>);
}

someFunction() OR throwException();<br /><br /></span>