PHP cannot locate the declaration of a class referred to in the code, often due to autoloading or namespace issues.
This error is thrown when PHP attempts to instantiate or reference a class that has not been loaded into memory. PHP stops script execution immediately.
Forgetting to include/require the file containing the class, namespace mismatch, or Composer autoloader not being loaded or updated.
1<?php2// Bug: User class is defined in another file but not included/imported3$user = new User(); // Fatal error: Class 'User' not found1<?php2// Fix 1: Require the file containing the class definition3require_once __DIR__ . '/src/User.php';4 5// Fix 2: Initialize Composer autoloader for PSR-4 autoloading namespaces6// require_once __DIR__ . '/vendor/autoload.php';7// use App\Models\User;8 9$user = new User();Simulate standard system builds to trigger compiler trace records and track memory crashes locally.
PHP tries to find the class 'User' in the global namespace but finds no declaration for it. It fails to trigger any autoloader and crashes.