Common predefined constants and instances in PHP

In PHP, you can use predefined constants to obtain information in PHP. Common predefined constants are as follows: In PHP, you can use predefined constants to obtain information in PHP.

Common predefined constants in PHP are as follows:

Constant name	Description
_ FILE __	The default constant is the PHP program file name.
_ LINE __	Default constant, which is the number of PHP programs
PHP_ OS	A built-in constant is the name of the operating system that executes the PHP parser.
PHP_VERSION	The built-in constant is the PHP program version.
TRUE	This constant is a true value.
FALSE	This constant is a dummy value.
NULL	A null value
E_ERROR	Error, resulting in termination of php script
E_WARNING	Warning, does not cause the php script to stop running
E_PARSE	Parsing error reported by the program parser
E_NOTICE	Non-critical errors, such as variable not initialized

Note: "" in FILE and LINE is two underscores rather than one "_".

Note: predefined constants starting with E _ are part of PHP error debugging.

PHP pre-defined constant instance:

The usage of predefined constants is no different from that of custom constants. The following uses a predefined constant to output information in PHP.

 Current number of PHP programs: ". LINE; echo"
Current PHP program version: ". PHP_VERSION; echo"
Current operating system: ". PHP_ OS;?>

The output result is similar to the following:

PHP program current file path: D: \ phpStudy \ www \ index. phpPHP program current number of lines: 3 current PHP program version: 5.6.27 current operating system: WINNT

Note: The results may vary depending on the operating system and software version used by each user.

The above are common predefined constants and instance details in PHP. For more information, see other related articles in the first PHP community!