php设置字符串的方法:1、通过单双引号定义字符串;2、通过heredoc定义字符串;3、通过nowdoc定义字符串。
推荐:《PHP视频教程》
PHP定义字符串的四种方式
1、简介
在PHP中这门语言中,因为是弱类型语言,因此使用变量时不需提前定义即可使用。
我们在使用php进行开发的时候,大多数使用双引号、单引号进行定义字符串。既然有这两种方式,那么他们之间肯定是有区别的。
并且,除了单双引号定义字符串这两种方式外,php还增加了heredoc和nowdoc这两种语法糖进行补充。
2、单引号与双引号
2.1、单引号
在单引号中,任何特殊字符都会按原样输出【除\\、\‘将会被转义输出】
eg.
<?php2 $var = 'this is a var!';3 echo '666$var666、\'、\"、\\、\n、\r、\t、\$';
从上面例子中我们可以明显看到,变量是没有被解析的;同时带反斜杠的转义字符仅仅只有单引号、反斜杠被转义输出了,其他的是直接输出。
在双引号中,遇到$将会解析该变量;
双引号中会转义反斜杠的转义字符;
转义字符代码 | 转义字符的含义 |
\ " | 双引号 |
\ ' | 单引号 |
\ \ | 反斜杠 |
\ n | 换行符 |
\ r | 回车符 |
\ t | 制表符 |
\ $ | 美元符号 |
eg.
<?php2 $var = 'this is a var!'; 3 echo "666$var 666、\'、\"、\\、\n、\r、\t、\$";
由上面例子我们可以知道,双引号中的变量被解析了,替换成字符串;其他带反斜杠的转义字符都进行了相应的转义。
2.3、单双引号之间的区别
以上两者主要区别:
1、双引号会替换变量的值,而单引号会把它当做字符串输出。
2、对于转义的支持
3、性能速度问题,由于双引号中的字符串需要检测是否含有$符号修饰的变量,因此从理论上讲,单引号是比较快的。
3、heredoc与nowdoc
3.1、heredoc
heredoc可以理解为不使用双引号来定义字符串,但效果与使用双引号一致。【此时双引号相当于普通字符】
语法要求:
1、开始标记和结束标记使用相同的字符串,通常以大写字母来写。
2、开始标记后不能出现空格或多余的字符。
3、结束标记必须顶头写,不能有缩进和空格,且在结束标记末尾要有分号 。
4、位于开始标记和结束标记之间的变量可以被正常解析,但是函数则不可以。
eg.
<?php $var = 'this is suifeng'; echo <<<"EOT" <!DOCTYPE html> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf8" /> <title>"随风"</title> </head> <body> 66666666666<br/> "666666666"<br/> $var<br/> \$var<br/> \n666<br> </body> </html> EOT;
从打印的结果我们可以看出:此时双引号仅仅只是一个普通字符;其他的效果和双引号的字符串效果一致。
3.2、nowdoc
同理,nowdoc是不使用单引号来定义,但效果相当于使用单引号来定义的字符串。【此时单引号相当于普通字符】
语法同heredoc
eg.
<?php $var = 'this is suifeng'; echo <<<'EOT' <!DOCTYPE html> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf8" /> <title>"随风"</title> </head> <body> '02020'<br/> \'<br/> 66666666666<br/> "666666666"<br/> $var<br/> \$var<br/> \n666<br> </body> </html> EOT;
注意:
定界符之后必须不能有任何字符【特别是空格字符有时会没注意到】,否则将会出错。
如上例中的EOT后面有空格就会报这个错误:【Parse error: syntax error, unexpected '
The above is the detailed content of How to set string in php. For more information, please follow other related articles on the PHP Chinese website!

The article compares ACID and BASE database models, detailing their characteristics and appropriate use cases. ACID prioritizes data integrity and consistency, suitable for financial and e-commerce applications, while BASE focuses on availability and

The article discusses securing PHP file uploads to prevent vulnerabilities like code injection. It focuses on file type validation, secure storage, and error handling to enhance application security.

Article discusses best practices for PHP input validation to enhance security, focusing on techniques like using built-in functions, whitelist approach, and server-side validation.

The article discusses strategies for implementing API rate limiting in PHP, including algorithms like Token Bucket and Leaky Bucket, and using libraries like symfony/rate-limiter. It also covers monitoring, dynamically adjusting rate limits, and hand

The article discusses the benefits of using password_hash and password_verify in PHP for securing passwords. The main argument is that these functions enhance password protection through automatic salt generation, strong hashing algorithms, and secur

The article discusses OWASP Top 10 vulnerabilities in PHP and mitigation strategies. Key issues include injection, broken authentication, and XSS, with recommended tools for monitoring and securing PHP applications.

The article discusses strategies to prevent XSS attacks in PHP, focusing on input sanitization, output encoding, and using security-enhancing libraries and frameworks.

The article discusses the use of interfaces and abstract classes in PHP, focusing on when to use each. Interfaces define a contract without implementation, suitable for unrelated classes and multiple inheritance. Abstract classes provide common funct


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

MantisBT
Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.

mPDF
mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),

Dreamweaver CS6
Visual web development tools

DVWA
Damn Vulnerable Web App (DVWA) is a PHP/MySQL web application that is very vulnerable. Its main goals are to be an aid for security professionals to test their skills and tools in a legal environment, to help web developers better understand the process of securing web applications, and to help teachers/students teach/learn in a classroom environment Web application security. The goal of DVWA is to practice some of the most common web vulnerabilities through a simple and straightforward interface, with varying degrees of difficulty. Please note that this software

ZendStudio 13.5.1 Mac
Powerful PHP integrated development environment