What does a php constant consist of?

PHP constant is an identifier of a simple value that cannot be changed in the script; after the constant value is defined, it cannot be changed anywhere else in the script. A constant consists of English letters, underscores, and numbers, but numbers cannot appear as the first letter. (The $ modifier is not required on the constant name).

Note: Constants can be used throughout the script.

Set PHP constants

To set constants, use define() function, functionSyntax is as follows:

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

This function has three parameters:

●name: required parameter, constant name, that is, identifier.

● Value: required parameter, the value of a constant.

●　case_insensitive: Optional parameter, if set to TRUE, this constant is case-insensitive. The default is case-sensitive.

In the following example we create a case-insensitive constant, the constant value is "Welcome to php.cn":

<?php
// 区分大小写的常量名
define("GREETING", "欢迎访问 php.cn");
echo GREETING;    // 输出 "欢迎访问 php.cn"
echo &#39;<br>&#39;;
echo greeting;   // 输出 "greeting"
?>

In the following example we create a case-insensitive constant, the constant value is "Welcome to php.cn":

<?php
// 不区分大小写的常量名
define("GREETING", "欢迎访问 php.cn", true);
echo greeting;  // 输出 "欢迎访问 php.cn"
?>

Constants are global

After a constant is defined, it defaults to a global variable and can be used throughout the Run the script anywhere it is used.

The following example demonstrates the use of constants within a function. Even if the constant is defined outside the function, the constant can be used normally.

<?php
define("GREETING", "欢迎访问 php.cn");
 
function myTest() {
    echo GREETING;
}
 
myTest();    // 输出 "欢迎访问 php.cn"
?>

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