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Predefined constants in PHP:
__FILE__
The name of the script file currently being processed. If used in an included file, its value is the included file, not the containing file name.
__LINE__
The current line number of the file being processed.
PHP_VERSION
indicates the current version of the PHP processor, such as: '3.0.8-dev'.
PHP_OS
The name of the operating system where the PHP processor is located, such as: '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 using __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!");
?>