blocks|key|2398128|text|null将被通过|type|ordered-list-item|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2398129|PHP中没有未定义的行为|2398130|通常测试是用empty($var)进行的，例如：Check(empty($foo)+?+null+:+$foo)，但取决于具体情况，isset可能更合适|2398131|isset所做的正是记录在案？？它测试作用域中是否存在这样一个变量，并且它的值与null不相同。|2398132|unstyled|entityMap|0|LINK|mutability|MUTABLE|url|http://php.net/manual/en/function.isset.php^0|0|4|0|0|6|B|O|W|1U|5|0|0|5|14|4|A|4|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|X|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|15|8|@$9|16|A|17|B|C]|$9|18|A|19|B|C]]|D|@$9|1A|A|1B|1|1C]]|E|$]]|$1|L|3|-4|5|M|7|1D|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

<ol>
<li><code>null</code> will be passed</li>
<li>There is no undefined behaviour in PHP AFAIK</li>
<li>Usually testing is done with <code>empty($var)</code>, e.g.: <code>Check(empty($foo) ? null : $foo)</code>, although depending on the circumstances <code>isset</code> may be more appropriate</li>
<li>What <code>isset</code> does is exactly <a href="http://php.net/manual/en/function.isset.php" rel="nofollow">documented</a> -- it tests if there is such a variable in scope and its value is not identical to <code>null</code></li>
</ol>

blocks|key|1201577|text|传递空，则会引发通知错误。|type|ordered-list-item|depth|inlineStyleRanges|entityRanges|data|1201578|不，函数只看到它的参数(它不在乎如何调用它)|1201579|您可以轻松地指定默认值--函数函数($mandatory，$optional+=‘默认值’)；|1201580|在函数参数上使用Isset是没有意义的，因为参数已经在函数签名中设置了。|1201581|unstyled|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|M|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|N|8|@]|9|@]|A|$]]|$1|H|3|-4|5|I|7|O|8|@]|9|@]|A|$]]]|J|$]]

<ol>
<li>NULL is passed, notice error is raised.</li>
<li>No, function sees only it's parameters (it doesn't care how it is being called)</li>
<li>You can specify default value easily - function func($mandatory, $optional = 'default value');</li>
<li>Isset withing a function on its parameters is pointless, because the parameters are already set in the functions signature.</li>
</ol>

blocks|key|1201629|text|当一个变量不存在并传递给函数(抑制错误)时，实际传递的是什么？|type|blockquote|depth|inlineStyleRanges|entityRanges|data|1201630|在这种情况下，您尝试从一个不存在的变量中读取。|unstyled|1201631|所以，你得到了null+--它被传递给函数。|offset|length|style|CODE|1201632|这个函数是否有任何未定义的行为？|1201633|但我并不认为--除非使用@运算符不是很好的实践。|1201634|entityMap^0|0|0|7|4|0|0|C|1|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$]]|$1|E|3|F|5|D|7|S|8|@$G|T|H|U|I|J]]|9|@]|A|$]]|$1|K|3|L|5|6|7|V|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|W|8|@$G|X|H|Y|I|J]]|9|@]|A|$]]|$1|O|3|-4|5|D|7|Z|8|@]|9|@]|A|$]]]|P|$]]

<blockquote>
 When a variable doesn't exist and is
 passed to the function (suppressing
 the error) what is actually passed?
</blockquote>

In this case, you try to read from a non-existent variable
 So, you get <code>null</code> -- which is passed to the function.

 

<blockquote>
 Is there any undefined behaviour that
 this function could exhibit?
</blockquote>

Not that I see -- except using the <code>@</code> operator is not quite a good practice.

blocks|key|2398225|text|您可以通过引用将变量传递给方法，方法是在声明函数时将&放在它的前面。然后，您只需检查它是否在函数中设置，而不必担心在传递未设置的值时是否会禁用警告。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2398226|function+Check(&$Variable,+$DefaultValue)+{
++++if(isset($Variable)+&&+$Variable+!=+""+&&+$Variable+!=+NULL)+{
++++++++return+$Variable;
++++}
++++else+{
++++++++return+$DefaultValue;
++++}
}

$a+=+Check($foo,+false);
$b+=+Check($bar,+"Hello");|code-block|syntax|javascript|2398227|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can pass the variable to the method by reference by putting an &amp; in front of it when declaring the function. Then you can just check if it set inside the function and not have to worry about suppressing warnings when passing the value that isn't set.

<pre><code>function Check(&amp;$Variable, $DefaultValue) {
 if(isset($Variable) &amp;&amp; $Variable != "" &amp;&amp; $Variable != NULL) {
 return $Variable;
 }
 else {
 return $DefaultValue;
 }
}

$a = Check($foo, false);
$b = Check($bar, "Hello");
</code></pre>

My code:
<pre><code>function Check($Variable, $DefaultValue) {
 if(isset($Variable) &amp;&amp; $Variable != &quot;&quot; &amp;&amp; $Variable != NULL) {
 return $Variable;
 }
 else {
 return $DefaultValue;
 }
}

$a = Check(@$foo, false);
$b = Check(@$bar, &quot;Hello&quot;);

//$a now equals false because $foo was not set.
//$b now equals &quot;Hello&quot; because $bar was not set.
</code></pre>
<ol>
<li>When a variable doesn't exist and is passed to the function (suppressing the error) what is actually passed?</li>
<li>Is there any undefined behaviour that this function could exhibit?</li>
<li>Is there a better way of wrapping the testing for variable existence and supplying a default value from a function?</li>
<li>What does <code>isset()</code> check under the hood when testing a variable?</li>
</ol>
<hr />
EDIT:
The default value is there to be user defined. Sometimes it will be a number, sometimes a string.

Passing unset variables to functions

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我的代码：function Check($Variable, $DefaultValue) {    if(isset($Variable) && $Variable != "" && $Variable != NULL) {        return $Variable;    }    else {       ...

问将未设置变量传递给函数
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