The difference between error messages and exception messages in php

What is an exception in PHP:

When the program is running, something unexpected happens, it is allowed to happen (you don’t want it to happen either) Abnormal situation) But it is an abnormal situation. According to our normal logic, errors should not occur, but errors that still occur are errors in logic and business processes, not compilation or syntax. error on.

What is an error in PHP: (Recommended learning: PHP programming from entry to proficiency)

belongs to php script Most of its own problems are caused by incorrect syntax and server environment, which makes the compiler fail to pass the check or even fail to run. Warning and notice are both errors, but their levels are different, and errors cannot be captured by try-catch.

The above statement has preconditions:

In PHP, because you cannot draw such conclusions in other languages, that is to say, exceptions and errors The saying has different meanings in different languages.

In PHP, any errors or abnormal code will be treated as errors and will not be thrown in the form of exceptions. However, there are also some situations where exceptions and errors will be thrown at the same time (it is said that, I No suitable example found).

In other words, if you want to automatically catch exceptions when the database connection fails, it will not work, because this is not an exception, but an error. But it's different in Java. It will capture many behaviors that are inconsistent with expectations as exceptions.

Is PHP exception handling useless?

We can see from the above analysis that PHP cannot actively throw exceptions, but you can manually throw exceptions. This is very speechless. If you know where it will happen, If something goes wrong, can't you just add if else to solve it? Why do you have to throw an exception manually? Since it can be thrown manually, it proves that this is not an exception, but is expected.

From my understanding, this is where PHP exception handling is useless (not necessarily right). Therefore, PHP's exception mechanism is not so perfect, but students who have used the framework all know this situation: it is okay for you to directly write the code at the beginning of the PHP "automatic" exception capture in the framework. Why is this?

Students who have read the source code know that there are three functions involved in the framework: register_shutdown_function, set_error_handler, set_exception_handler, three black technologies. Through these functions, we can realize PHP's false automatic capture of exceptions and errors.

Throw errors in the form of exceptions (cannot be thrown completely)

From the above explanation, we know that errors in php cannot be captured in the form of exceptions, but we need to Let them throw, which has expanded the scope of influence of try-catch. We talked about the set_error_handler() method earlier. What is it used for? It captures errors, so we can use it to capture errors, and then Then throw it in the form of an exception, ok, try the following writing:

<?php
    set_error_handler(&#39;error&#39;);
    function error($type, $message, $file, $line)
    {
        throw new \Exception($message . &#39;错误当做异常&#39;);
    }

    $num = 0;
    try {
        echo 1/$num;

    } catch (Exception $e){
        echo $e->getMessage();
    }
?>

In PHP it is best not to simply throw exceptions directly where errors may occur. In some frameworks, the above is rewritten. Methods, exceptions and errors can be thrown normally

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