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PHP Tutorial
The difference between single quotes and double quotes for getting started with PHP_PHP Tutorial
The difference between single quotes and double quotes for getting started with PHP_PHP Tutorial
【1】单引号和双引号在处理变量的时候做法：
括在双引号内的变量会解释出值，但是括在单引号内则不做处理，直接输出；
<?php $var = 'my name is huige'; echo "$var"; //结果是:my name is huige echo '$var'; //结果是:$var ?>
【2】如果在语句中要转义操作，那么就一定要用双引号了。
比如，转定义单引号时，写成这样的话：
$a = ‘He\’s name is Huige.’ ;
程序会把He\’s name is Tom.原封不动的显示出来，如果这样写：
$a = “He\’s name is Huige.”;
程序就会显示：He’s name is Tom.
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下面列举写转义字符的含义（当在双引号内使用这些字符时，它们具有特殊的含义）
====================================================
下面在来一个例子来演示了使用单引号和双引号之间的区别：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>引号</title> </head> <body> <?php // 设置必要要的变量: $quantity = 30; // 出售30件产品. $price = 119.95; // 单价. $taxrate = .05; // 5%的发票税. // 计算总额: $total = $quantity * $price; $total = $total + ($total * $taxrate); // Calculate and add the tax. // 格式化总额: $total = number_format ($total, 2); // 打印结果使用双引号： echo "<h3>使用双引号：</h3>"; echo "<p>你所出售的 <b>$quantity</b> 件产品,成本单价为 <b>\$$price</b>. 加上发票税，总额为 <b>\$$total</b>.</p>\n"; // 打印结果使用单引号： echo '<h3>使用单引号：</h3>'; echo '<p>你所出售的 <b>$quantity</b> 件产品,成本单价为 <b>\$$price</b>. 加上发票税，总额为 <b>\$$total</b>.</p>\n'; ?> </body> </html>
最后结果如下图：
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1、这个例子中用双引号打印结果，是这篇文章（php入门变量之数字）中一个例子的单引号打印结果的另一个解决方法。
2、在这个例子中由于双引号是能打印出变量的，所以我们把要打印的东西全部放到双引号中，但是唯一的问题就是打印$符号问题了，要打印出$符号，我们直接进行转义即可。
3、同时在这两种引号内使用换行符（\n ）会有什么区别呢？？？
答：当把换行符（\n ）置于双引号内时，它会在HTML 源代码中创建一个新行。当把它置于单引号内时，它会直接打印出\和n。
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FAQ：
1、在运行效率上单引号和双引号也是有区别的，一般来说单引号的运行速度会比较快，双引号会比较慢，原因在于双引号要先查找语句中是否有变量，而单引号则不用，因此，如果语句中没有代入变量尽量采用单引号。这是写程序一种习惯，时刻想着提高程序的效率。
2、当利用PHP 打印HTML 时，使用单引号最容易。
echo '<table width="80% " border="0" cellspacing="2" cellpadding="3" align="center">';
如果想使用双引号打印出这段HTML 代码，将不得不对字符串中的所有双引号进行转义。
echo "<table width=\"80%\" border= \"0\" cellspacing=\"2\" cellpadding=\"3\" align=\" center\">";
3、如果你仍然不清楚这两种引号之间的区别，可以使用双引号，这样不太可能出问题。
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