PHP常用的預定義常數如下：
#| Description | |
| 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
echo "PHP程序当前文件路径名:".FILE;
echo "<br >PHP程序当前行数:".LINE;
echo "<br >当前PHP程序的版本:".PHP_VERSION;
echo "<br >当前操作系统:".PHP_OS;
?>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
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