PHP Tutorial

🔒 PHP Constants

Constants in PHP are like variables, but once they are defined, their values cannot be changed. They're great for storing fixed values like configuration settings or mathematical values.

🛠️ How to Define a Constant

You can define a constant in PHP using the define() function:

<?php
  define("SITE_NAME", "Technorank");
  echo SITE_NAME; // Output: Technorank
?>
  

✨ Constant Characteristics

• Constants do not require a $ symbol.
• Once defined, constants cannot be changed or undefined.
• Constants are globally accessible throughout the script.

📦 Example with Conditional Use

Using constants to check conditions or configure app behavior:

<?php
  define("DEBUG_MODE", true);

  if (DEBUG_MODE) {
    echo "Debugging is enabled!";
  }
?>
  

🎯 Magic Constants in PHP

PHP also provides special built-in constants called Magic Constants, like:

• __FILE__ → Full path of the file.
• __LINE__ → Current line number.
• __DIR__ → Directory of the file.

<?php
  echo "This file is located at: " . __FILE__;
?>
  

📱 Responsive Tip:

🚫 Can Constants Be Overwritten?

No. Once a constant is defined using define(), trying to redefine it will not change its value:

<?php
  define("SITE_VERSION", "1.0");
  define("SITE_VERSION", "2.0"); // This will not overwrite the first one.
  echo SITE_VERSION; // Output: 1.0
?>
  

🧠 Summary

• Use define("NAME", value); to create constants.
• No $ symbol is needed before constant names.
• Once set, they can’t be changed.
• Accessible globally — use them wisely!