不能在try catch块之外使用属性

Question

I am trying to use properties inside try catch blocks. The try catch blocks are inside classes. I want to extend a specific class, making it the subclass of the class which handles exceptions. The problem is, that when I try to use those variables from the subclass, it always says undefined. I have to delete both of classes in order to catch the properties. After reading some other answers here by adding a return statement (I added return 1) outside, inside of the try catch block, it doesn't seem to work and it always says undefined variable. Any help?

The language is php

The source code without classes works perfect:

    try
    {
        //$pdo variable to insert PDO object information
        $pdo = new PDO('mysql:host=localhost;dbname=studenti', 'root', '');

        //Set php to catch exceptions
        $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

        //Set UTF-8 for character encodings
        $pdo->exec('SET NAMES "utf8"');
    }
    //Catch error if unable to connect
    catch(PDOException $e)
    {
        //error variable
        $error = 'Unable to connect with database. ' . $e->getMessage();

        //include file once and show on screen error message
        include_once $_SERVER['DOCUMENT_ROOT'] . '/inc/error.inc.php';
        //Exit and don't process further
        exit();
    }

    //Another Exception handling
    try
    {
        //Select statement
        $sql = 'SELECT * FROM dega';
        $select = $pdo->query($sql);
    }
    catch(PDOException $e)
    {
        //error variable
        $error = 'Unable to select table. ' . $e->getMessage();

        //include file once and show on screen error message
        include_once $_SERVER['DOCUMENT_ROOT'] . '/inc/error.inc.php';

        //Exit and don't process further
        exit();
    }

The source code with classes doesn't work:

<?php
    //PDO class, connection with MySQL database
    class Connect
    {
        function connection()
        {
        $pdo = null;
            try
            {
                //$pdo variable to insert PDO object information
                $pdo = new PDO('mysql:host=localhost;dbname=studenti', 'root', '');

                //Set php to catch exceptions
                $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

                //Set UTF-8 for character encodings
                $pdo->exec('SET NAMES "utf8"');
            }
            //Catch error if unable to connect
            catch(PDOException $e)
            {
                //error variable
                $error = 'Unable to connect with database. ' . $e->getMessage();

                //include file once and show on screen error message
                include_once $_SERVER['DOCUMENT_ROOT'] . '/inc/error.inc.php';
                //Exit and don't process further
                exit();
            }
        }
    }

    class Select extends Connect
    {
        function selection()
        {
            //Another Exception handling
            try
            {
                //Select statement
                $sql = 'SELECT * FROM dega';
                $select = $pdo->query($sql);
            }
            catch(PDOException $e)
            {
                //error variable
                $error = 'Unable to select table. ' . $e->getMessage();

                //include file once and show on screen error message
                include_once $_SERVER['DOCUMENT_ROOT'] . '/inc/error.inc.php';

                //Exit and don't process further
                exit();
            }
        }
    }

    //Output if successful
    $error = 'Database connection established.';
    include $_SERVER['DOCUMENT_ROOT'] . '/inc/error.inc.php';
?>

Answer 1

1. You have no subclass. Object Inheritance
2. You have no properties. Properties

Read about Classes and Objects.

---

class Connect
    {
    protected $pdo = null;

    public function connection()
        {
        $pdo = null;
        try
            {
            $this->pdo = new PDO('mysql:host=localhost;dbname=studenti', 'root', '');
            $this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
            $this->pdo->exec('SET NAMES "utf8"');
            } catch (PDOException $e)
            {
            $error = 'Unable to connect with database. ' . $e->getMessage();
            include_once $_SERVER['DOCUMENT_ROOT'] . '/inc/error.inc.php';
            exit();
            }
        }
    }

class Select extends Connect
    {

    function selection()
        {
        try
            {
            $sql = 'SELECT * FROM dega';
            $select = $this->pdo->query($sql);
            } catch (PDOException $e)
            {
            $error = 'Unable to select table. ' . $e->getMessage();
            include_once $_SERVER['DOCUMENT_ROOT'] . '/inc/error.inc.php';
            exit();
            }
        }
    }