Constants for beginners to PHP

One:What is a constant

After a constant value is defined, it cannot be changed anywhere else in the script

A constant is an identifier of a simple value , a constant consists of English letters, underscores, and numbers, but numbers cannot appear as the first letter. (Constant names do not need to be added with the $ modifier)

Note: Constants can be used throughout the script

2:Set PHP constants

Use define() function

Syntax format:

bool define ( string $name , mixed $value [, bool $case_insensitive = false ] )

The define function has 3 parameters

1.name: required parameter, constant name, i.e. identifier

2.value: required parameter, constant value

3 .case_insensitive optional parameter, if set to TRUE, this constant is case-insensitive. The default is case-sensitive

'; echo greeting; // 输出 "greeting" ?>

Note: This is case-sensitive, so an error will be reported

Let’s write a case-insensitive one

Note: This will output "Welcome to taobao.com" without reporting an error

Constants can be used outsidewithout quotation marksonly Scalars can be used

In addition, the system has also prepared some built-in constants for us as shown in the figure below