Commonly used predefined constants and examples in PHP

PHPYou can use predefined constants to obtain information in PHP.

The commonly used predefined constants in PHP are as follows:

##Constant nameDescription##__FILE____LINE__PHP_OS PHP_VERSIONTRUEFALSENULLE_ERRORE_WARNING

The default constant is the PHP program file name
The default constant is the number of PHP program lines
Built-in constants refer to the name of the operating system that executes the PHP parser
Built-in constants refer to the version of the PHP program
The constant is a true value
The constant is a false value
A null value
Error, causing the php script to terminate
Warning will not cause the php script to terminate
E_PARSE	Parse errors, reported by the program parser
E_NOTICE	Non-critical errors, such as variables not initialized

Note: The "" in FILE and LINE are two underscores, not one "_".

Description: The predefined constants starting with E_ are the error debugging part of PHP.

PHP predefined constant example:

# #There is no difference in usage between predefined constants and user-defined constants. The following uses predefined constants to output information in PHP.

PHP程序当前行数:".LINE;
    echo "
当前PHP程序的版本:".PHP_VERSION;
    echo "
当前操作系统:".PHP_OS;
?>

Output results similar to the following:

PHP程序当前文件路径名:D:\phpStudy\www\index.php
PHP程序当前行数:3
当前PHP程序的版本:5.6.27
当前操作系统:WINNT

Note: Depending on the operating system and software version used by each user, the results may not be the same.

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