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PHP 5 Constants

After constant value is defined elsewhere in the script not to be changed.

PHP constants

Constant is an identifier for a simple value. This value can not be changed in the script.

A constant consists of English letters, underscores, and numbers, but the numbers do not appear as the first letter. (Constant names do not need to add $ modifier).

Note: Constant throughout the script can be used.

Setting PHP constants

Setting constants using define () function, the function syntax is as follows:

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

This function takes three arguments:

  • name: Required parameters, constant name, that flag.
  • value: the value of mandatory parameters, constants.
  • case_insensitive: optional parameter, if set to TRUE, the constant is case-insensitive. The default is case-sensitive.

The following example we create a case-sensitive constant, constant value of "Welcome to":

// 区分大小写的常量名
define("GREETING", "欢迎访问");
echo GREETING;    // 输出 "欢迎访问"
echo '<br>';
echo greeting;   // 输出 "greeting"

The following example we create a case-insensitive constant, constant value of "Welcome to":

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

Constants are global

After defining the constants, the default is a global variable that can be used anywhere in the entire run of the script.

The following example demonstrates the use of constants within a function, even if constants are defined in the outer function can be used normally constant.

define("GREETING", "欢迎访问");

function myTest() {
    echo GREETING;
myTest();    // 输出 "欢迎访问"