Getting Started with PHP: How to Use Define_PHP Tutorial

PHP pre-defines several constants and provides a mechanism to define them yourself 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.

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."
?>

Examples using __FILE__ and __LINE__

＜?php
function report_error(＄file, ＄line, ＄message) {
echo "An error occurred in ＄file on line ＄line: ＄message.";
}
report_error(__FILE__,__LINE__, "Something went wrong!");
?>

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