Alaa Amer

Lesson 7: PHP Magic Constants

PHP Magic Constants are powerful built-in constants that provide contextual information during code execution. Unlike regular constants, their values change depending on where they are used.

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What Are Magic Constants?

Magic Constants are predefined constants in PHP that start and end with double underscores (__). They return specific information like file names, line numbers, class names, and more.

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Most Common PHP Magic Constants

1. __LINE__

Returns the current line number in the file.
📌 Example:

echo "You are on line " . __LINE__;

2. __FILE__

Returns the full path and filename of the file.
📌 Example:

echo "File path: " . __FILE__;

3. __DIR__

Returns the directory of the file.
📌 Example:

echo "Directory: " . __DIR__;

4. __FUNCTION__

Returns the name of the function.
📌 Example:

function test() { echo "Function name: " . __FUNCTION__; } test();

5. __CLASS__

Returns the class name.
📌 Example:

class MyClass { public function show() { echo "Class: " . __CLASS__; } }

6. __METHOD__

Returns the class method name.
📌 Example:

class MyClass { public function show() { echo "Method: " . __METHOD__; } }

7. __NAMESPACE__

Returns the current namespace.
📌 Example:

namespace MyApp; echo "Namespace: " . __NAMESPACE__;

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When Should You Use Them?

• For debugging and logging errors.

• To get dynamic file paths.

• When documenting code automatically.

• While working on dynamic class loaders.

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Benefits of Magic Constants

• ✅ Easy to track and debug code.
• ✅ Add flexibility and automation.
• ✅ Improve maintainability and structure.

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Conclusion

PHP Magic Constants give developers access to useful runtime information. When used wisely, they help you write smarter, cleaner, and more maintainable PHP code.

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