blocks|key|4824838|text|我的问题是，有没有什么方法可以在不两次声明变量的情况下做到这一点？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4824839|？|blockquote|4824840|4824841|4824842|不，如果不做两次检查，就无法正确完成此操作。I+hate+it,+too.|offset|length|4824843|解决这个问题的一种方法是在一个中心点将所有相关的GET变量导入到某种类型的数组或对象中(大多数MVC框架会自动执行此操作)，并设置以后需要的所有属性。(而不是跨代码访问请求变量。)|4824844|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/1960509/isset-and-empty-make-code-ugly^0|0|0|0|0|M|F|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$]]|$1|E|3|-4|5|6|7|W|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|X|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|Y|8|@]|9|@$I|Z|J|10|1|11]]|A|$]]|$1|K|3|L|5|6|7|12|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]]]

<blockquote>
 My question is, exist any way to do this without declare the variable twice?
</blockquote>

No, there is no way to do this correctly without doing two checks. <a href="https://stackoverflow.com/questions/1960509/isset-and-empty-make-code-ugly">I hate it, too.</a> 

One way to work around it would be to import all relevant GET variables at one central point into an array or object of some sort (Most MVC frameworks do this automatically) and setting all properties that are needed later. (Instead of accessing request variables across the code.)

blocks|key|1226175|text|可悲的是，这是唯一的方法。但是有一些方法可以处理更大的数组。例如，如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1226176|$required+=+array('myvar',+'foo',+'bar',+'baz');
$missing+=+array_diff($required,+array_keys($_GET));|code-block|syntax|javascript|1226177|变量$missing现在包含$_GET数组中缺少的必需值的列表。您可以使用$missing数组向访问者显示一条消息。|1226178|或者你可以使用类似这样的东西：|1226179|$required+=+array('myvar',+'foo',+'bar',+'baz');
$missing+=+array_diff($required,+array_keys($_GET));
foreach($missing+as+$m+)+{
++++$_GET[$m]+=+null;
}|1226180|现在，每个必需的元素至少都有一个默认值。您现在可以使用if($_GET‘’myvar‘==+'something')，而不用担心没有设置密钥。|1226181|更新|offset|length|style|BOLD|1226182|清理代码的另一种方法是使用一个检查是否设置了值的函数。|1226183|function+getValue($key)+{
++++if+(!isset($_GET[$key]))+{
++++++++return+false;
++++}
++++return+$_GET[$key];
}

if+(getValue('myvar')+==+'something')+{
++++//+Do+something
}|1226184|entityMap^0|0|0|0|0|0|0|0|2|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|12|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|13|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|14|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|15|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|16|8|@$Q|17|R|18|S|T]]|9|@]|A|$]]|$1|U|3|V|5|6|7|19|8|@]|9|@]|A|$]]|$1|W|3|X|5|D|7|1A|8|@]|9|@]|A|$E|F]]|$1|Y|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]]|Z|$]]

Sadly that's the only way to do it. But there are approaches for dealing with larger arrays. For instance something like this:

<pre><code>$required = array('myvar', 'foo', 'bar', 'baz');
$missing = array_diff($required, array_keys($_GET));
</code></pre>

The variable $missing now contains a list of values that are required, but missing from the $_GET array. You can use the $missing array to display a message to the visitor.

Or you can use something like that:

<pre><code>$required = array('myvar', 'foo', 'bar', 'baz');
$missing = array_diff($required, array_keys($_GET));
foreach($missing as $m ) {
 $_GET[$m] = null;
}
</code></pre>

Now each required element at least has a default value. You can now use if($_GET['myvar'] == 'something') without worrying that the key isn't set.

Update

One other way to clean up the code would be using a function that checks if the value is set.

<pre><code>function getValue($key) {
 if (!isset($_GET[$key])) {
 return false;
 }
 return $_GET[$key];
}

if (getValue('myvar') == 'something') {
 // Do something
}
</code></pre>

blocks|key|1226201|text|好的，你可以只使用if($_GET['myvar']+==+'something')，因为这个条件假设变量也存在。如果不是，则表达式也将导致false。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1226202|我认为在上面这样的条件语句中做这件事是可以的。真的没什么坏处。|1226203|entityMap^0|9|X|1Y|5|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|P|8|@]|D|@]|E|$]]]|I|$]]

Well, you could get by with just <code>if($_GET['myvar'] == 'something')</code> since that condition presumes that the variable also exists. If it doesn't, the expression will also result in <code>false</code>.

I think it's ok to do this inside conditional statements like above. No harm done really.

blocks|key|4824941|text|为什么不创建一个这样做的函数，将你想要检查的变量转换成一个真实的变量，例如。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4824942|function+_FX($name)+{+
++if+(isset($$name))+return+$$name;
++else+return+null;+
}|code-block|syntax|javascript|4824943|然后你做_FX('param')+==+'123'，这只是一个想法|offset|length|style|CODE|4824944|entityMap^0|0|0|4|L|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

why not create a function for doing this, convert the variable your want to check into a real variable, ex. 

<pre><code>function _FX($name) { 
 if (isset($$name)) return $$name;
 else return null; 
}
</code></pre>

then you do <code>_FX('param') == '123'</code>, just a thought

blocks|key|1226224|text|正如mellowsoon建议的那样，您可以考虑使用这种方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1226225|required+=+array('myvar'+=>+"defaultValue1",+'foo'+=>+"value2",+'bar'+=>+"value3",+'baz'+=>+"value4");
$missing+=+array_diff($required,+array_keys($_GET));
foreach($missing+as+$key+=>+$default++)+{
++++$_GET[$key]+=+$default++;
}|code-block|syntax|javascript|1226226|设置默认值，并将未接收的参数设置为默认值:)|1226227|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

As mellowsoon suggest, you might consider this approach:

<pre><code>required = array('myvar' =&gt; "defaultValue1", 'foo' =&gt; "value2", 'bar' =&gt; "value3", 'baz' =&gt; "value4");
$missing = array_diff($required, array_keys($_GET));
foreach($missing as $key =&gt; $default ) {
 $_GET[$key] = $default ;
}
</code></pre>

You put the default values and set the not recieved parameters to a default value :)

blocks|key|1973223|text|我一直使用自己有用的函数exst()，它可以自动声明变量。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|1973224|示例：|1973225|$element1+=+exst($arr["key1"]);
$val2+=+exst($_POST["key2"],+'novalue');


/**+
+*+Function+exst()+-+Checks+if+the+variable+has+been+set+
+*+(copy/paste+it+in+any+place+of+your+code)
+*+
+*+If+the+variable+is+set+and+not+empty+returns+the+variable+(no+transformation)
+*+If+the+variable+is+not+set+or+empty,+returns+the+$default+value
+*
+*+@param++mixed+$var
+*+@param++mixed+$default
+*+
+*+@return+mixed+
+*/

function+exst(+&+$var,+$default+=+"")
{
++++$t+=+"";
++++if+(+!isset($var)++%7C%7C+!$var+)+{
++++++++if+(isset($default)+&&+$default+!=+"")+$t+=+$default;
++++}
++++else++{++
++++++++$t+=+$var;
++++}
++++if+(is_string($t))+$t+=+trim($t);
++++return+$t;
}|code-block|syntax|javascript|1973226|entityMap^0|C|6|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|R|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|S|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

I use all time own useful function exst() which automatically declare variables.

Example -

<pre><code>$element1 = exst($arr["key1"]);
$val2 = exst($_POST["key2"], 'novalue');


/** 
 * Function exst() - Checks if the variable has been set 
 * (copy/paste it in any place of your code)
 * 
 * If the variable is set and not empty returns the variable (no transformation)
 * If the variable is not set or empty, returns the $default value
 *
 * @param mixed $var
 * @param mixed $default
 * 
 * @return mixed 
 */

function exst( &amp; $var, $default = "")
{
 $t = "";
 if ( !isset($var) || !$var ) {
 if (isset($default) &amp;&amp; $default != "") $t = $default;
 }
 else { 
 $t = $var;
 }
 if (is_string($t)) $t = trim($t);
 return $t;
}
</code></pre>

blocks|key|3413710|text|我在尝试中发现的一个解决方案是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3413711|if($x=&$_GET["myvar"]+==+"something")
{
++++//+do+stuff+with+$x
}|code-block|syntax|javascript|3413712|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|$]]

A solution that I have found from playing around is to do:

<pre><code>if($x=&amp;$_GET["myvar"] == "something")
{
 // do stuff with $x
}
</code></pre>

blocks|key|1968458|text|没有官方参考，但当我尝试这样做时，它起作用了：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1968459|if+(isset($_GET['myvar'])+==+'something')|code-block|syntax|javascript|1968460|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|$]]

No official reference but it worked when I tried this:

<pre><code>if (isset($_GET['myvar']) == 'something')
</code></pre>

blocks|key|1973263|text|<?php

function+myset(&$var,$value=false){
++++if(isset($var)):
++++++++return+$var+==+$value+?+$value+:+false;
++++endif;
++++return+false;
}

$array['key']+=+'foo';

var_dump(myset($array['key'],'bar'));+//bool(false)

var_dump(myset($array['key'],'foo'));//string(3)+"foo"

var_dump(myset($array['baz'],'bar'));//bool(false)+|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1973264|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>&lt;?php

function myset(&amp;$var,$value=false){
 if(isset($var)):
 return $var == $value ? $value : false;
 endif;
 return false;
}

$array['key'] = 'foo';

var_dump(myset($array['key'],'bar')); //bool(false)

var_dump(myset($array['key'],'foo'));//string(3) "foo"

var_dump(myset($array['baz'],'bar'));//bool(false) 
</code></pre>

blocks|key|1223740|text|这与公认的答案类似，但改为使用in_array。在这种情况下，我更喜欢使用empty()。我还建议使用PHP+5.4.0%2B中提供的新的速记数组声明。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1223741|$allowed+=+["something","nothing"];
if(!empty($_GET['myvar'])+&&+in_array($_GET['myvar'],$allowed)){..}|code-block|syntax|javascript|1223742|下面是一次检查多个值的函数。|1223743|$arrKeys+=+array_keys($_GET);
$allowed+=+["something","nothing"];

function+checkGet($arrKeys,$allowed)+{+
++++foreach($arrKeys+as+$key+)+{
++++++++if(in_array($_GET[$key],$allowed))+{
++++++++++++$values[$key];
++++++++}
++++}
++++return+$values;
}|1223744|entityMap|0|LINK|mutability|MUTABLE|url|http://php.net/releases/5_4_0.php^0|F|8|11|7|1F|9|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@$9|11|A|12|1|13]]|E|$]]|$1|F|3|G|5|H|7|14|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|15|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|16|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

This is similar to the accepted answer, but uses <code>in_array</code> instead. I prefer to use <code>empty()</code> in this situation. I also suggest using the new shorthand array declaration which is available in <a href="http://php.net/releases/5_4_0.php" rel="nofollow">PHP 5.4.0</a>+.

<pre><code>$allowed = ["something","nothing"];
if(!empty($_GET['myvar']) &amp;&amp; in_array($_GET['myvar'],$allowed)){..}
</code></pre>

Here is a function for checking multiple values at once.

<pre><code>$arrKeys = array_keys($_GET);
$allowed = ["something","nothing"];

function checkGet($arrKeys,$allowed) { 
 foreach($arrKeys as $key ) {
 if(in_array($_GET[$key],$allowed)) {
 $values[$key];
 }
 }
 return $values;
}
</code></pre>

blocks|key|4825176|text|如果您正在寻找一行程序来检查您还不确定是否设置了变量的值，这是可行的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4825177|if+((isset($variable)+?+$variable+:+null)+==+$value)+{+}|code-block|syntax|javascript|4825178|唯一可能的缺点是，如果您正在测试true/false+-+null将被解释为等于false。|offset|length|style|CODE|4825179|entityMap^0|0|0|G|4|L|5|T|4|14|5|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]|$I|T|J|U|K|L]|$I|V|J|W|K|L]|$I|X|J|Y|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|N|$]]

If you're looking for a one-liner to check the value of a variable you're not sure is set yet, this works:

<pre><code>if ((isset($variable) ? $variable : null) == $value) { }
</code></pre>

The only possible downside is that if you're testing for <code>true</code>/<code>false</code> - <code>null</code> will be interpreted as equal to <code>false</code>.

blocks|key|1973313|text|从PHP7开始，您可以使用Null+Coalescing+Operator+??来避免双重引用：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1973314|$_GET['myvar']+=+'hello';
if+(($_GET['myvar']+??+'')+==+'hello')+{
++++echo+"hello!";
}|code-block|syntax|javascript|1973315|输出：|1973316|hello!|1973317|一般而言，表达式|1973318|$a+??+$b|1973319|等同于|1973320|isset($a)+?+$a+:+$b|1973321|entityMap|0|LINK|mutability|MUTABLE|url|http://php.net/manual/en/language.operators.comparison.php^0|12|2|D|O|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|14|8|@$9|15|A|16|B|C]]|D|@$9|17|A|18|1|19]]|E|$]]|$1|F|3|G|5|H|7|1A|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1B|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|1C|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1D|8|@]|D|@]|E|$]]|$1|Q|3|R|5|H|7|1E|8|@]|D|@]|E|$I|J]]|$1|S|3|T|5|6|7|1F|8|@]|D|@]|E|$]]|$1|U|3|V|5|H|7|1G|8|@]|D|@]|E|$I|J]]|$1|W|3|-4|5|6|7|1H|8|@]|D|@]|E|$]]]|X|$Y|$5|Z|10|11|E|$12|13]]]]

As of PHP7 you can use the <a href="http://php.net/manual/en/language.operators.comparison.php" rel="noreferrer">Null Coalescing Operator</a> <code>??</code> to avoid the double reference:

<pre><code>$_GET['myvar'] = 'hello';
if (($_GET['myvar'] ?? '') == 'hello') {
 echo "hello!";
}
</code></pre>

Output:

<pre><code>hello!
</code></pre>

In general, the expression

<pre><code>$a ?? $b
</code></pre>

is equivalent to

<pre><code>isset($a) ? $a : $b
</code></pre>

I have (or not) a variable <code>$_GET['myvar']</code> coming from my query string and I want to check if this variable exists and also if the value corresponds to something inside my if statement:

What I'm doing and think is not the best way to do:

<code>if(isset($_GET['myvar']) &amp;&amp; $_GET['myvar'] == 'something')</code>: do something

My question is, exist any way to do this without declare the variable twice?

That is a simple case but imagine have to compare many of this <code>$myvar</code> variables.

PHP: Check if variable exist but also if has a value equal to something

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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我有(或没有)一个来自我的查询字符串的变量$_GET['myvar']，我想检查这个变量是否存在，以及它的值是否与if语句中的某个值相对应：我所做的和所想的并不是最好的方法：if(isset($_GET['myvar']) && $_GET['myvar'] == 'something')：做点什么我的问题是，有没有办...

问PHP:检查变量是否存在，以及是否有等于某个值的值
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问PHP:检查变量是否存在，以及是否有等于某个值的值EN