blocks|key|3011029|text|它在中提到过|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3011030|3011031|赋值表达式的值是赋值的值。也就是说，"$a+=+3“的值是3。|blockquote|offset|length|style|CODE|3011032|3011033|3011034|因此，如果将true分配给$c，则$c+=+...将生成true；如果将false分配，则将生成false。|3011035|这也是迭代查询结果的原因|3011036|while(($row+=+mysql_fetch_array(...)))|code-block|syntax|javascript|3011037|很管用。|3011038|entityMap^0|0|0|T|1|0|0|0|6|4|D|2|H|8|S|4|10|5|1C|5|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|10|8|@$F|11|G|12|H|I]]|9|@]|A|$]]|$1|J|3|-4|5|6|7|13|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|14|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|15|8|@$F|16|G|17|H|I]|$F|18|G|19|H|I]|$F|1A|G|1B|H|I]|$F|1C|G|1D|H|I]|$F|1E|G|1F|H|I]|$F|1G|G|1H|H|I]]|9|@]|A|$]]|$1|N|3|O|5|6|7|1I|8|@]|9|@]|A|$]]|$1|P|3|Q|5|R|7|1J|8|@]|9|@]|A|$S|T]]|$1|U|3|V|5|6|7|1K|8|@]|9|@]|A|$]]|$1|W|3|-4|5|6|7|1L|8|@]|9|@]|A|$]]]|X|$]]

It is mentioned in <a href="http://php.net/manual/en/language.operators.assignment.php" rel="nofollow">Assignment Operators</a>:

<blockquote>
 The value of an assignment expression is the value assigned. That is, the value of "$a = 3" is <code>3</code>.
</blockquote>

So <code>$c = ...</code> will result in <code>true</code> if <code>true</code> is assigned to <code>$c</code> and in <code>false</code> if <code>false</code> is assigned.

That is also the reason why iterating over query results

<pre><code>while(($row = mysql_fetch_array(...)))
</code></pre>

works.

blocks|key|3297145|text|它并不总是与“成功”相呼应。PHP首先将mysql_connect的结果赋给$to，然后计算$to的布尔值。但最好使用这种方式来确保可理解性：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3297146|$c+=+mysql_connect($host,+$user,+$pass)
if($to)+{
++++echo+'Success';
}+else{
++++echo+'Failure';
}|code-block|syntax|javascript|3297147|entityMap^0|K|D|12|3|1A|3|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|U|8|@]|D|@]|E|$]]]|L|$]]

It does not always echo 'Success'. PHP first assigns the result of <code>mysql_connect</code> to <code>$to</code> then evaluates boolean value of <code>$to</code>. But it's better to use this way to ensure the understandability:

<pre><code>$c = mysql_connect($host, $user, $pass)
if($to) {
 echo 'Success';
} else{
 echo 'Failure';
}
</code></pre>

blocks|key|1396276|text|如果有疑问，构建一个测试用例！|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|1396277|构建一个测试用例：|1396278|if+(+$c+=+true+)+{
++echo+'Success';
}+else+{
++echo+'No+Success';
}|code-block|syntax|javascript|1396279|在线运行以下代码：http://codepad.org/jxylNzOu|1396280|您将注意到，第一个代码块仅在条件出现true时才会执行(或者在被询问时，PHP的计算结果为true+)，因此它不会询问某个值是否成功应用于$c，而是询问应用于$c的值是否为true。|CODE|1396281|关于您的特定示例的...|1396282|在您尝试打开到MySQL的连接的情况下，如果已建立连接，则$c将为true，从而导致运行if-statement的第一个块。否则，如果没有建立连接，$c将为false，使得if-statement的条件为false，从而导致else块的运行。|1396283|根据mysql_connect()的the+documentation，此函数可以返回以下两项中的一项。|1396284|1396285|+MySQL链接标识符(如果连接是made)|ordered-list-item|1396286|FALSE，，则表示无法建立连接。|1396287|1396288|因此，下面的代码示例之间没有区别|1396289|$conn+=+mysql_connect(+$host,+$user,+$pass+);
if+(+$conn+)+{+/*...*/+}|1396290|和|1396291|if+(+$conn+=+mysql_connect(+$host,+$user,+$pass+)+{
++/*...*/
}|1396292|entityMap|0|LINK|mutability|MUTABLE|url|http://codepad.org/jxylNzOu|1|http://php.net/manual/en/function.mysql-connect.php^0|0|F|0|0|0|9|R|0|0|I|4|19|4|1X|2|27|2|2E|4|0|9|3|0|T|2|X|4|18|C|22|2|2E|C|34|4|0|2|F|I|H|1|0|0|0|0|5|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1M|8|@$9|1N|A|1O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1P|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1Q|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1R|8|@]|D|@$9|1S|A|1T|1|1U]]|E|$]]|$1|O|3|P|5|6|7|1V|8|@$9|1W|A|1X|B|Q]|$9|1Y|A|1Z|B|Q]|$9|20|A|21|B|Q]|$9|22|A|23|B|Q]|$9|24|A|25|B|Q]]|D|@]|E|$]]|$1|R|3|S|5|6|7|26|8|@$9|27|A|28|B|C]]|D|@]|E|$]]|$1|T|3|U|5|6|7|29|8|@$9|2A|A|2B|B|Q]|$9|2C|A|2D|B|Q]|$9|2E|A|2F|B|Q]|$9|2G|A|2H|B|Q]|$9|2I|A|2J|B|Q]|$9|2K|A|2L|B|Q]]|D|@]|E|$]]|$1|V|3|W|5|6|7|2M|8|@$9|2N|A|2O|B|Q]]|D|@$9|2P|A|2Q|1|2R]]|E|$]]|$1|X|3|-4|5|6|7|2S|8|@]|D|@]|E|$]]|$1|Y|3|Z|5|10|7|2T|8|@]|D|@]|E|$]]|$1|11|3|12|5|10|7|2U|8|@$9|2V|A|2W|B|Q]]|D|@]|E|$]]|$1|13|3|-4|5|6|7|2X|8|@]|D|@]|E|$]]|$1|14|3|15|5|6|7|2Y|8|@]|D|@]|E|$]]|$1|16|3|17|5|J|7|2Z|8|@]|D|@]|E|$K|L]]|$1|18|3|19|5|6|7|30|8|@]|D|@]|E|$]]|$1|1A|3|1B|5|J|7|31|8|@]|D|@]|E|$K|L]]|$1|1C|3|-4|5|6|7|32|8|@]|D|@]|E|$]]]|1D|$1E|$5|1F|1G|1H|E|$1I|1J]]|1K|$5|1F|1G|1H|E|$1I|1L]]]]

When in doubt, build a test-case!

Build a test-case:

<pre><code>if ( $c = true ) {
 echo 'Success';
} else {
 echo 'No Success';
}
</code></pre>

Run this online: <a href="http://codepad.org/jxylNzOu" rel="nofollow">http://codepad.org/jxylNzOu</a>

You'll note that the first block will only be executed if the conditions turn up <code>true</code> (or what PHP evaluates as <code>true</code> when asked), so it's not asking if a value was successfully applied to <code>$c</code>, but rather whether the value applied to <code>$c</code> is <code>true</code>.

Regarding your specific example...

If your case, where you're attempting to open a connection to MySQL, <code>$c</code> will be <code>true</code> if the connection is made, resulting in the first block of the <code>if-statement</code> being ran. Otherwise, if no connection is made, <code>$c</code> will be false, making the condition of the <code>if-statement</code> false, resulting in the running of the <code>else</code> block.

According to <a href="http://php.net/manual/en/function.mysql-connect.php" rel="nofollow">the documentation</a> for <code>mysql_connect()</code>, one of two things can be returned from this function.

<ol>
<li>A MySQL Link Identifier (if a connection is made)</li>
<li><code>FALSE</code>, indicating a failure to make a connection.</li>
</ol>

So there's no difference between the following code examples

<pre><code>$conn = mysql_connect( $host, $user, $pass );
if ( $conn ) { /*...*/ }
</code></pre>

And

<pre><code>if ( $conn = mysql_connect( $host, $user, $pass ) {
 /*...*/
}
</code></pre>

blocks|key|1396418|text|PHP是一种“弱类型”语言，这意味着php不需要(也不支持)变量的显式类型声明。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1396419|注意consufe或将0+1计算为true/false+(布尔值)|1396420|以本例为例：|1396421|$s+=+"0";+//String+s+=+'0'
$res+=+strstr($s,'0');+//Search+the+character+zero+into+the+string+$s
if+($res){
++echo+"Zero+found!";
}else{
++echo+"Zero+not+found!"
}
//Hey!!+Whats+up!!??+Zero+is+not+found!|code-block|syntax|javascript|1396422|这是因为strstr函数的返回值为FALSE，在某些情况下会产生意想不到的结果。|offset|length|style|CODE|1396423|正确的方法是使用Not+Identical运算符!==，其中比较value和类型|BOLD|1396424|前面的示例应该是：|1396425|$s+=+"0";+//String+s+=+'0'
$res+=+strstr($s,'0');+//Search+the+character+zero+into+the+string+$s
if+($res+!==+FALSE){//Check+for+value+AND+type
++echo+"Zero+found!";
}else{
++echo+"Zero+not+found!"
}
//yeah+now+it+works!|1396426|因此，在您的情况下，我会将if语句编写为：|1396427|if(($c+=+mysql_connect($host,+$user,+$pass))+!==+FALSE){
+echo+'Success';
}else{
+echo+'Failure';
}|1396428|entityMap^0|0|0|0|0|4|6|H|5|0|8|D|O|3|12|2|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|13|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|14|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|15|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|16|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|17|8|@$M|18|N|19|O|P]|$M|1A|N|1B|O|P]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1C|8|@$M|1D|N|1E|O|P]|$M|1F|N|1G|O|P]|$M|1H|N|1I|O|S]]|9|@]|A|$]]|$1|T|3|U|5|6|7|1J|8|@]|9|@]|A|$]]|$1|V|3|W|5|H|7|1K|8|@]|9|@]|A|$I|J]]|$1|X|3|Y|5|6|7|1L|8|@]|9|@]|A|$]]|$1|Z|3|10|5|H|7|1M|8|@]|9|@]|A|$I|J]]|$1|11|3|-4|5|6|7|1N|8|@]|9|@]|A|$]]]|12|$]]

PHP is a "weakly typed" language which means php doesn't require (nor support it for that matter) explicit type declaration of variables.

Pay attention to consufe or evaluate 0 1 as true/false (boolean value)

Take this case as sample:

<pre><code>$s = "0"; //String s = '0'
$res = strstr($s,'0'); //Search the character zero into the string $s
if ($res){
 echo "Zero found!";
}else{
 echo "Zero not found!"
}
//Hey!! Whats up!!?? Zero is not found!
</code></pre>

This is because zero, which is the returned value of the function <code>strstr</code>, is evaluated as <code>FALSE</code> producing in some cases unexpected results.

The correct way is to use the <code>Not Identical</code> operator <code>!==</code> where value and type is compared

The previous example should be:

<pre><code>$s = "0"; //String s = '0'
$res = strstr($s,'0'); //Search the character zero into the string $s
if ($res !== FALSE){//Check for value AND type
 echo "Zero found!";
}else{
 echo "Zero not found!"
}
//yeah now it works!
</code></pre>

So in your case I would write the if statement as:

<pre><code>if(($c = mysql_connect($host, $user, $pass)) !== FALSE){
 echo 'Success';
}else{
 echo 'Failure';
}
</code></pre>

This seems like a very mysterious part of PHP to me, and I was wondering if someone could clarify because the manual doesn't seem to include this (or I just couldn't find it anywhere).

What would some of these things return?

<pre><code>if($c = mysql_connect($host, $user, $pass)){
 echo 'Success';
}else{
 echo 'Failure';
}
</code></pre>

Would this always echo 'Success' because $c is successfully assigned to true or false? I'm wondering if I can do this or if I have to define $c on the previous line.

Thanks.

What does $var = value actually return?

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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这对我来说似乎是PHP的一个非常神秘的部分，我想知道是否有人可以澄清一下，因为手册中似乎没有包括这一点(或者我在任何地方都找不到它)。其中的一些东西会返回什么呢？if($c = mysql_connect($host, $user, $pass)){ echo 'Success';}else{ echo 'Failur...

问$var = value实际返回什么？
EN

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问$var = value实际返回什么？EN