PHP Predefined and Magic Constants Cheat Sheet (PHP 8.4 Ready)

A categorized reference of the most useful constants in PHP with descriptions, error masks, and sample outputs for PHP 8.3 and PHP 8.4.

PHP provides built-in constants for filesystem operations, compile-time metadata, runtime environment information, error levels, and stream handles. These constants are available globally without importing namespaces or requiring setup.

Filesystem and Path Constants

Constant	Description	Example Output
`DIRECTORY_SEPARATOR`	Path separator (`/` on Unix, `\` on Windows)	`/`
`PATH_SEPARATOR`	Include path separator (`:` on Unix, `;` on Windows)	`:`
`__FILE__`	Full filesystem path and filename of the current file	`/var/www/html/index.php`
`__DIR__`	Directory path containing the current file	`/var/www/html`
`__LINE__`	Current line number in the executing file	`42`

Magic Compile-Time Constants

Magic constants are resolved at compile time, introducing zero runtime performance overhead:

Constant	Description	Example Output
`__FUNCTION__`	Current function name	`calculateTotal`
`__CLASS__`	Current class name with namespace	`App\Models\Order`
`__TRAIT__`	Current trait name	`App\Traits\HasLabel`
`__METHOD__`	Current class method name	`App\Services\PaymentService::charge`
`__NAMESPACE__`	Current namespace	`App\Services`

PHP Environment and System Limits

Constant	Description	Example Output
`PHP_VERSION`	Full PHP version string	`8.4.1`
`PHP_MAJOR_VERSION`	Major version integer	`8`
`PHP_MINOR_VERSION`	Minor version integer	`4`
`PHP_RELEASE_VERSION`	Patch release integer	`1`
`PHP_OS`	Operating system string from PHP build	`Linux`, `WINNT`, `Darwin`
`PHP_OS_FAMILY`	Portable operating system group	`Linux`, `Windows`, `BSD`, `Darwin`
`PHP_SAPI`	Server API interface type	`cli`, `fpm-fcgi`, `apache2handler`
`PHP_EOL`	Correct newline character for the host OS	`\n` or `\r\n`
`PHP_INT_MAX`	Maximum integer supported by host architecture	`9223372036854775807`
`PHP_INT_MIN`	Minimum integer supported by host architecture	`-9223372036854775808`
`PHP_FLOAT_MAX`	Maximum floating-point number	`1.7976931348623E+308`
`PHP_FLOAT_MIN`	Minimum positive normalized floating-point number	`2.2250738585072E-308`

Error Reporting Masks

Constant	Description	Category
`E_ERROR`	Fatal runtime errors that halt execution	Fatal
`E_WARNING`	Non-fatal runtime warnings	Warning
`E_PARSE`	Compile-time parse/syntax errors	Fatal
`E_NOTICE`	Runtime notices about potential issues	Notice
`E_CORE_ERROR`	Fatal errors generated by PHP core startup	Fatal
`E_CORE_WARNING`	Warnings generated by PHP core startup	Warning
`E_COMPILE_ERROR`	Fatal errors generated by the Zend script engine	Fatal
`E_COMPILE_WARNING`	Warnings generated by the Zend script engine	Warning
`E_USER_ERROR`	User-generated fatal error via `trigger_error()`	Fatal
`E_USER_WARNING`	User-generated warning via `trigger_error()`	Warning
`E_USER_NOTICE`	User-generated notice via `trigger_error()`	Notice
`E_RECOVERABLE_ERROR`	Catchable fatal error	Fatal (Catchable)
`E_DEPRECATED`	Runtime notices about deprecated features	Warning
`E_USER_DEPRECATED`	User-generated deprecation notice	Warning
`E_ALL`	Bitmask covering all supported error levels	Aggregate

File Upload Error Codes

When processing $_FILES['upload']['error'], compare against these constants instead of magic numbers:

Constant	Code	Description
`UPLOAD_ERR_OK`	`0`	File uploaded successfully
`UPLOAD_ERR_INI_SIZE`	`1`	File exceeds `upload_max_filesize` in `php.ini`
`UPLOAD_ERR_FORM_SIZE`	`2`	File exceeds `MAX_FILE_SIZE` specified in HTML form
`UPLOAD_ERR_PARTIAL`	`3`	File was only partially uploaded
`UPLOAD_ERR_NO_FILE`	`4`	No file was selected for upload
`UPLOAD_ERR_NO_TMP_DIR`	`6`	Missing temporary upload folder on server
`UPLOAD_ERR_CANT_WRITE`	`7`	Failed to write file to server disk
`UPLOAD_ERR_EXTENSION`	`8`	A PHP extension stopped the file upload

CLI Stream Constants

Available automatically in Command Line Interface (CLI) scripts:

Constant	Description	Direction
`STDIN`	Open stream resource reading from standard input	Input
`STDOUT`	Open stream resource writing to standard output	Output
`STDERR`	Open stream resource writing to standard error	Output

Summary

Use PHP_OS_FAMILY instead of comparing against individual PHP_OS strings for cross-platform compatibility.
Use UPLOAD_ERR_* constants when handling file uploads for descriptive error checking.
Leverage magic constants (__DIR__, __CLASS__, __METHOD__) for zero-overhead compile-time introspection.