The difference between single quotes and double quotes for getting started with PHP

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The difference between single quotes and double quotes for getting started with PHP_PHP Tutorial

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Jul 13, 2016 am 10:35 AM

aspnetsoftware programming

【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 = &lsquo;He\&rsquo;s name is Huige.&rsquo; ;

程序会把He\’s name is Tom.原封不动的显示出来，如果这样写：

    $a = &ldquo;He\&rsquo;s name is Huige.&rdquo;;

程序就会显示：He’s name is Tom.

====================================================

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 id="使用双引号">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 id="使用单引号">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：

================================================================

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。

================================================================

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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