致命错误：未捕获错误：未找到类“应用程序\数据库”

Question

I try to learn oop but in my first class it gives me this error.

Database class

<?php
namespace App;

class Database
{
   ...
}

in my functions.php

<?php
require 'helpers.php';
require 'connection.php';
use App\Database;
...

Class under the "app" folder and it's namespace is "App". Why I'm getting this error ?

Answer 1

You either need to include the file, or use an AutoLoader. AutoLoaders tell PHP where a class can be found, as PHP needs to know the file.

Autoloaders are fully explained in the PHP documentation: https://secure.php.net/manual/en/language.oop5.autoload.php

Example from the mentioned documentation:

<?php
spl_autoload_register(function ($class_name) {
    include $class_name . '.php';
});

$obj  = new MyClass1();
$obj2 = new MyClass2(); 
?>

In this case spl_autoload_register is used to register the autoloader. The autoloader is a function which takes the class name, and includes the necessary class. For example you can use the autoloader function as used above, in which case the class name needs to be identical to the filename. This is a quite simple example, but a more advanced autoloader could check if files exist, check multiple locations, etc...

Examples are mentioned in the comments on your original question.

note: You will find other sources mentioning the __autoload($class) function. This function does exactly the same, but will be removed from PHP in future updates. Therefore, you are better off using spl_autoload_register