Five minutes to show you what exception handling is in PHP

In the previous article, I brought you "You must understand how to add image watermarks in PHP", which gave you a detailed introduction to how to add watermarks in PHP through examples. This article In this article, we will continue to look at the relevant knowledge of error handling in PHP. I hope it can help everyone!

Error and exception handling in PHP are very commonly used in PHP. In our daily development, we will definitely encounter, for example, forgetting to add a semicolon. , function names are written incorrectly or functions are redefined, etc. There are many errors. If errors can be found during the development process, it will definitely be very beneficial to our development.

Therefore, rational use of a process when developing a project will help us find and correct errors to speed up development. Then let's take a look at how to understand our error handling. You can also learn through the free "php Error Handling" teaching video.

Exception handling class in PHP

In PHP, there is a built-in exception handling class, which is Exception, this class contains some exception handling functions, which can capture program exceptions and errors.

The following are the more commonly used functions in this class:

• getTraceAsString(): Returns the function that has been formatted into a string. Information generated by the getTrace() function

• __toString(): String information that generates exceptions, it can be overloaded. Note that the front of this function is two underscores

• getMessage(): Returns the abnormal message content

• getLine(): Returns the code line number where the error occurred

• getCode(): Returns the exception code in numeric form

• getFile(): Returns the file name where the exception occurred

• getTrace(): Returns the backtrace() array

Capture exceptions in the program

Exceptions in the program generally do not show themselves. At this time we can The purpose of catching exceptions in the program is achieved through the try catch statement and the throw keyword.

The try catch statement is similar to the flow control statement. The throw keyword can throw an exception. We can capture the exception in the program through a structure similar to conditional selection. The syntax format of the try catch statement is as follows:

try{
    // 可能出现异常或错误的代码，比如文件操作、数据库操作等
}catch(Exception $a){    // $a 为一个异常类的对象
    // 输出错误信息
}

When we need to catch program exceptions, we need to put the code that needs to be caught into the try code block. In the above syntax, each try should have at least one and The corresponding catch. When the try code block does not catch a matching exception, the code will jump to the last catch and continue.

Exceptions generated in it can be thrown out by the throw statement and captured by catch. When an exception occurs, the code behind it will no longer continue to execute.

The example is as follows:

<?php
    try{
        $err = &#39;抛出异常信息，并跳出 try 语句块&#39;;
        if(is_dir(&#39;./demo&#39;)){
            echo &#39;这里是一些可能会发生异常的代码&#39;;
        }else{
            throw new Exception($err, 20211020);   // 抛出异常
        }
        echo &#39;上面抛出异常的话，这行代码将不会执行，转而执行 catch 中的代码。<br>&#39;;
    }catch(Exception $e){
        echo &#39;捕获异常：&#39;.$e->getMessage().&#39;<br>错误代码：&#39;.$e->getCode().&#39;<br>&#39;;
    }
    echo &#39;继续执行 try catch 语句之外的代码&#39;;
?>

Output result:

In the above example, try to judge through the try statement Is there a directory named demo in the current directory? The directory does not exist, so the throw keyword is executed and an exception is thrown. After the exception is found and thrown, the remaining statements of the try statement will not be executed.

Create your own exception class

You can define some exceptions in advance in PHP, because PHP rarely takes the initiative Throw exceptions. When exceptions are defined in advance, we can use if-else to judge possible exceptions and throw exceptions manually. In PHP, we can often use the exception classes we create ourselves.

Examples are as follows:

<?php
class emailException extends Exception{
    function __toString(){
        return "<b>email is null</b>file:".$this->getFile().&#39;,line:&#39;. $this->getLine();
    }
}
class nameException extends Exception{
}
?>

In the above example, two exception classes are defined, both of which inherit from the Exception base class.

In actual business, we will also throw different exceptions according to different needs. Examples are as follows:

function reg($reg) {
    if (empty($reg['email'])) {
        throw new emailException("emaill is null", 1);
    }
    if(empty($reg['name'])) {
        throw new nameException("name is null", 2);
     }
}

When executing business code, you can use the if statement to determine whether the exception will occur. Where it occurs, then manually throw the exception, and distribute different exceptions to different exception classes through statements; in the following example, different exceptions are captured according to different situations. When the first catch catches the exception, Even if other exceptions still exist in the program, other catch code blocks will be skipped. Regardless of whether there is an exception in the program, the statements in the finally finally will be executed. An example is as follows:

try{
    $reg = array('phone'=>'1888888888');
    reg($reg);
} catch(emailException $e) {
    echo $e;
} catch(nameException $e) {
    echo 'error msg:' .$e->getMessage().'error code:'.$e->getCode();
} finally {
    echo ' finally';
}

If you want to know more about PHP, you can click on "PHP Video Tutorial" to learn!

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