Constants in PHP

Source: Internet
Author: User
Tags constant define function
PHP pre-defines several constants and provides a mechanism to define them at runtime. Constants and variables are basically the same. The difference is that constants must be defined using the DEFINE function. Once a constant is defined, it cannot be redefined.

PHP pre-defined constants:
_ FILE __
The script file name being processed. If it is used in an included file, its value is the included file, not the file name.

_ LINE __
The current number of objects being processed.

PHP_VERSION
Indicates the current version of the PHP processor, for example, '3. 0.8-Dev '.

PHP_ OS
The operating system name of the PHP processor, for example, 'Linux '.

TRUE
True Value
FALSE
False value

You can use the DEFINE function to DEFINE more constants.

For example, define constants:
<? Php
Define ("CONSTANT", "Hello world .");
Echo CONSTANT; // outputs "Hello world ."
?>
Example of _ FILE _ and _ LINE _
<? Php
Function report_error ($ file, $ line, $ message ){
Echo "An error occured in $ file on line $ line: $ message .";
}
Report_error (_ FILE __,__ LINE __, "Something went wrong! ");
?>
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