PHP示意字符串的单引号和双引号有什么区别?定界符和双引号区别
PHP表示字符串的单引号和双引号有什么区别?定界符和双引号区别?
(1)单引号和双引号的区别?
1、可以使用转义的范围不同,单引号只能转义单引号\',双引号除了单引号不能转义,其他\"\n\r\t都能。
2、双引号中能解析php变量,单引号不能。即"我的名字叫$name"。
但是在字符串中使用变量,我们指导$表示变量开始,但是没有指定变量结束位置,所以如果不是放在末尾的话会出错。
解决方案:
1、放在末尾。后面没有东西了,自然就正确。
2、变量后面增加空格。遇到空格默认结束。
3、使用大括号{}。
4、使用连接符“.”或“,”,连接字符和变量。
(2)定界符和双引号的区别?
定界符,就是$str=
1、定界符必须成对。
2、右定界符必须顶格,不能有任何缩进。
3、定界符开始和结束符的后面不能有任何东西。
定界符和双引号区别
1、定界符看起来格式易读。
2、定界符输出的结果保留了格式。
(3)以下是变量和常量的一些说法:
<?php //php常量,可以被修改删除 $name="张三"; echo $name; echo "<br />"; $name="李四"; echo $name; echo "<br>"; //Notice: Undefined variable: name in... unset($name); echo $name; echo "<br>"; //常量定义后,不可被修改和删除 //常量命名建议:(1)大写;(2)多字母时用下划线连接 define("AGE", 29); echo AGE; //如果常量是如下-_-,那么直接echo的话是有语法错误,需要换成另一种访问常量的方式 echo constant("AGE"); //Notice: Constant AGE already defined in... define("AGE", 30); //Parse error: syntax error, unexpected ')', expecting :: (T_PAAMAYIM_NEKUDOTAYIM) in... unset(AGE); //php执行结束后,会释放所有变量和常量占用的内容,由系统回收?>

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