Notes.txt

PHP Basic
====================
    Write any PHP code inside HTML body inside <?php  ?> tag.

    To print in browser
    --------------------
    Use echo. 

    If you have to concatinate any variable with the string, then use dot(.) after the variable 
    and then write the variable name. In case of JAVA it is + 

    To declare a Variable
    ----------------------
    Use $ and the variable name. Ex - $abc , $My_name, $gae


PHP Bult-in Function
==========================
    Math Functions(predefined)
    --------------------------
        pow(base, power); - echo pow(2,7); = 2 to the power 7
        rand(); = Return random Number , rand(1,1000) = return number between 1 to 1000
        sqrt(number) = return square root of 100
        ceil(4.22) = round up to the upper number, i.e answer here is 5
        floor(4.88) = rond up to the down number. Answer here is 4
        round(number) = round up to the nearest number. round(4.4) = 4 and round(4.7) = 5

        ** Ref php.net/manual/ref.math.php

    String Functions(predefined)
    ----------------------------
        strlen(string) = return the length of the string
        strtoupper(string) = change all the letter of the string to Uper case.
        strtolower(string) = change all the letter of the string to Lower case.

        ** Ref php.net/ref.strings

    Array Functions(Predefined)
    ----------------------------
        max($array_name) = return max number in the Array
        min($array_name) = return min in the array
        echo print_r($array_name) = this will print whole array in key-value pair format
        sort($array_name) = return sorted array

        ** Ref php.net/manual/en/ref.array.php

FORM in PHP
=====================
    There are super Global variables in PHP for form data handling. Such as $_POST & $_GET
    Super global variables are available in our script globally, any where inside the function or outside of it.
    Here $_POST nad $_GET an associative Arrays which contains all the field name and value entered in it.

    We can then use isset() function to check if the form is submitted or not and then run a piece of
    code if the form is submitted, else don't run it. if(isset($_POST['submit'])){}, here submit is
    the name attribute value of submit type field.

    Then we can get the data of each field of the form by $_POST['Name_Of_field']. Or if we
    echo $_POST we'll get all the data input from the form as an associative array.

    We can use $_GET to get all the GET type method values, For example if any value is passed through the url.

    Example-
        If in 38.getSuperGlobal.php file we write
            <?php 
                print_r($_GET);   //As $_GET and $_POST are associative arrays
            ?>

        and then if we hit a url, localhost/38.getSuperGlobal.php
            we'll get out put Array(). i.e empty array
        But if we hit a url, localhost/38.getSuperGlobal.php?id=100&name=Sibajee    
            we'll get o/p as Array([id]=>10 [name]=>sibajee)


DataBase in PHP
=======================
    To do datbase operations we use API in PHP like mysqli api.

    Make Connection
    ----------------
        There is a function to make connection to the database, i.e
            mysqli_connect('server_url', 'username', 'password', 'dataBase_name'); This function return a Connection Object

            In our case(for phpmyadmin) 
                server_url = 'localhost' (as we are using database installed in our own computer)
                username = 'root'
                passwrod = ''  (Empty, As it is not created) 
                database_name = 'test'   

        So, $connection = mysqli_connect('localhost', 'root', '', 'test');
            if($connection){----}

        If connection could not established then there is a function in mysqli, i.e die('message')
        which will output a message and exit the script automatically.No line after die() will be executed if
        this die() get a chance to execute.

        if($connection)
            echo "Connection Established";
        else
            die("Connection failed");

    Run Query
    ----------------
        To run any query on DB we have to make use of the mysqli_query function.
        mysqli_query('connection_object' , 'query_String') which returns a boolean value. true(success), false(failed)

        Ex - 
            $query = "insert into users values('Sibajee', 2000)";
            $result = mysqli_query($connection, $query); 
            if($result)
                echo "Query Executed";
            else
                die("Query failed");

    Get Error
    -----------
        To get error we have functions. like

        mysqli_connect_error() ---> This will print the error occured during connection.
        (or)
        mysqli_error($connection); --> This will print the error occured on query After connection established.

        so we can write 
            if($result)
                echo "Query Executed";
            else
                die("Query failed".mysqli_error($connection));


    Read Data from DB
    ----------------------
        By running "Select * from Db" query we will get all the data of the DB. Let's store it in 
        a variable.
            $query = "select * from users";
            $result = mysqli_query($connection, $query); 

        Now to show each row of the db, we have to iterate the $result.

        For this we have two mysqli function i.e 
            mysqli_fetch_row($result).  ->this function return each row of the DB as normal array.
            mysqli_fetch_assoc($result). ->This function return each row of DB as an Associative array,
                                            Where the key will be the table metadata like id,username.

            Iterate it
            
            1st Case :  while($row = mysqli_fetch_row($result){
                            print_r($row);
                        }) 

                    Result here is : Array ( [0] => 1 [1] => Sibajee Ray [2] => chetana ) Array ( [0] => 2 [1] => Subbu [2] => cbag )

                
            2nd Case  : while($row = mysqli_fetch_assoc($result){
                            print_r($row);
                        }) 

                    Result here is : Array ( [id] => 1 [username] => Sibajee Ray [password] => chetana ) Array ( [id] => 2 [username] => Subbu [password] => cbag )

Include File in PHP
====================
    We can include any php file to another file and directly can use the variables and
    functions of the included file without creating those in the current file again.

    To include one file, we have to use (include "path/file_name.php") inside the <?php tag. And then ;

    Ex-
        <?php include "file1.php"; ?>
        <?php
            echo "file1_variable";
        ?>

        (or)

        <?php include "file1.php";
            echo "file1_variable";
        ?>


PHP Security
==============

    mysqli_real_escape_string($connection, $username)
    --------------------------------------------------
        We should pass our username or any other strings through this function to sanitise it from the 
        SQL Injections. This Function prevent any sql queries through the form parameters and also alow us to
        insert escape characters.
        Ex-
            in username we can not pass Sibajee's as it has 's.
            But if we will pass the username with the escape characters through this func, it will allow us to use that

        Ex-
            $username = $_POST['username'];
            $password = $_POST['password'];
            $username = mysqli_real_escape_string($connection, $username);
            $password = mysqli_real_escape_string($connection, $password);
            $query = "insert into users values('$username','$password')" ;


    PASSWORD ENCRYPTION
    ------------------------
        1st of all change the max lenght of password field of the DB to at least 200. 
        Bcoz the encrypted passwrod can be very long.

        We will use crypt() function to change the user password to long, unpredictable, alpha-numeric character
        before we save it to the DB. By seeing DB also nobody can get the real passwrod of a user.

        We need another parameter i.e salt, bcoz crypt() create weaker password without salt.

        Salt is hashing to change the password.We need to use a selected(There are many, see the reference) hash type to salt the password.
        We will use blowfish hashing here. 

        crypt('','') has two parameters. 1st one compusory and 2nd is optional. Where
            1st parameter is out password which we want to encrypt.
            2nd parameter is salt, which contains hash parameter(hash format) to ditinguish which hashing we'll use 
                and somearbitary string.

                The hash format u can find in the documentation. For blowfish hashing
                $hashFormat = "$2y$";

                With this hash format we have to add a number which state that how many time the hashing should
                be done to encrypt the password.

                So, $hashFormat = "$2y$10$"; (Runs 10 times)

        So let's $salt = $hashFormat."AnyStringOfLengthMoreThan22CanBeUsed".

        Now $encryptedPassword = crypt($password, $salt);

        Ex- Final code is
        ----------------
            $password = $_POST['password'];

            $hashFormat = "$2y$10$";
            $salt = $hashFormat."AnyStringOfLengthMoreThan22CanBeUsed";
            $encryptedPassword = crypt($password, $salt);

        Encrypted password Verifiction during Login
        --------------------------------------------
            Encrypted password that is saved in DB always contains the salt as a prefix.

            So if we call again pass the th encrypted password through crypt() as salt, it will extract the 
            1st 22 characters and get the exact salt we used to encrypt it.
            So to verify the passwrod we can write

                if ($encryptedPassword == crypt($password, $encryptedPassword)) {
                    echo "Success! Valid password";
                } else {
                    echo "Invalid password";
                } 

                (or)

                function validate_pw($password, $encryptedPassword){
                    return crypt($password, $encryptedPassword)==$encryptedPassword; //return true or false
                }


        *Ref php.net/manual/function.crypt.php

Cookies and Session in PHP
===========================
    Both are almost same. Session works along with the cookies. But there are limited space(around 2mb) for 
    cookies and we can use space in hard disk as much as we want to store sessions.

    Cookie is the permanent Data saved in the user's browser, won't expire before the expiry date we set.
    Session is not permanent. For each browser session one session file will be created in the server submitted
        which will be cleared once we close the browser.

    Cookies
    ---------
        All the cookies are saved in a super global variable called $_COOKIE which is an associative array.

        setcookie()
        -------------
        setcookie() is the function used to set new cookie to $_COOKIE. It has 3 parameters.
            1st --> Name of Cookies
            2nd --> The value of the cookie, could be anything
            3rd --> expiration of the cookie. When do u want it to expire.
                    For expiration we use time() funtion. If we want it to be there for a week, then 
                    $expiration = time() + (60*60*24*7);  (In seconds)

        example-
            $name= "TestCookie";
            $value = 100;
            $expiration = time() + (60*60*24*7);
            setcookie($name, $value, $expiration);

        To check all the cookies that is saved in google chrome browser, 
        go to setting->show advanced setting->content setting->All cookies and site data"

        Get Cookie value
        ------------------
            To get the cookie value we simply have to echo the associative array $_COOKIE with your cookie name.

            echo $_COOKIE["TestCookie"]; //It will print only the value of the cookie.

    Session
    -----------
        In case of session, data does not be saved in user browser. If we start a session, a cookie will be
        created in the user browser which will cintent the session ID. But a data file will be created on the
        server which will save all the data belongs to the same browser in that file. When we start a session,
        PHP start a new session for a browser and the session will be valid till the browser open. Once closed,
        session will be stoped.

        Start and store value in $_SESSION
        -------------------------------
        session_start(); 
        $_SESSION["name"] = "Sibajee";
        $_SESSION["age"] = 25;
        $_SESSION["greet"] = "Hello Sibajee";

        We can store unlimited key-value pairs. All the value will be stored in a file in the server and 
        the ID to of the session will be stored in the user browser as cookies named PHPSESSID, which will
        help to refer to the corresponding session file of the browser.

        To get value stored in the $_SESSION from another php file
        ------------------------------------------------------------
        This $_SESSION file will be available to the every php file of our program, But we have to start
        Session in every file to access that by session.start(); It will create new session only when session 
        is not created for the browser, else it will use the already existing session file and it will get the
        reference to that session file from the cookie saved in it named PHPSESSID.

        session_start();
        echo $_SESSION["name"];
        echo $_SESSION["age"];

    NOTE: Session for a browser will be cleared once we close the browser. And after closing the browser
    we can't access the Session values before we stored it again.

Obejct Oriented PHP
============================
    Class describe an Object which has two types of data, Properties and function.

    class is the key word to define a class in php.

       class Class_name {

       }

    class_exists("Class_name") is a predefined function to check if the class is already defined or not.

    Declare Properties nad Methods in a Class
    -------------------------------------------
        Properties
        --------------
            Class properties can be defined with "var" keyword and then variable name with $ sign as usual.

            var $no_of_wheels = 4;
            var $color = "white";

        Methods
        -----------
        We can create normal function inside a class. Function inside a class is called method, not a function.

        class Car {

            function move_wheels(){
                echo "Wheels started moving";
            }
        }

        we can check if the method exist or not by predefined function method_exists("class_name", "method_name") function.

    Instanciate a Class & call the class methods and properties
    ------------------------------------------------------------
        We can create object of php class simply by "new" keyword and class constructor and then can save it on a variable.

        $bmw = new Car();
        $mercedes = new Car();

        To call a method of the class on any object of it, we use arrow operator.
            $bmw -> move_wheels();

        To call any property of the object also we use arrow operator.
            echo $bmw -> color;
                But here we don't write $ infront of the property name. Only color, not $color.

    $this
    ---------
        Inside a class, $this keyword refers the current object of the class.

        class Car {
            var $no_of_wheels = 4;

            function changeWheels() {
                $this->no_of_wheels = 10;
            }
        }

        $truck = new Car();
        $truck -> changeWheels();
        echo $truck->no_of_wheels; 
        
        Here the O/P will be 10, not 4. Bcoz we have called changeWheels() on truck.
        And in this changeWheel function we used $this->no_of_wheels, 
        means no_of_wheels property of current object, means the object on which the method is called.


    Inheritance
    ============
        Child class can inherit properties and methods from parent class.

        We use "extends" keyword to inherit parent data.

        <?php
            class Vehicle {
                var $wheelcount = 4;
                var $color = "white";

                function moveWheels() {
                    echo "Wheels are moving";
                }
            }

            $bmw = new Vehicle();

            class Truck extends Vehicle {

                //Nothing is overriden here
            }

            $truckObject = new Truck();

            echo $truckObject->wheelcount; //* This will print 4. Truck class does not has wheelcount property. It will print it's parent class property, i.e Vehicle class.

            $truckObject->moveWheels(); // this will execute Vehicle class moveWheel() method.

        ?>

        Constructors
        --------------
            Contructor gets executed every time we create object of a class. it assigns the default values to the object properties.

            In PHP we write constructor exactly as the function, But that function name should be __construct.

                ex- 
                    function __construct(){

                    }

            So if we have any common action we want to do everytime we create object then we should write those codes inside constructor.

            We can also assign values to the Object through it's constructor while creating new object.
                
                class Vehile {
                    function __construct($wheel, $color){
                        $this->wheelsCount = $wheel;
                        $this->color = $color;
                    }
                }
                and then while creating object, pass 2 parameters --->  $bmw = new Vehicle(4, "white");

            *constructor can not be overloaded in php. We can write only one constructor in a class which may have Zero argumenmt,
            Or may have any no of arguments.

        Overriding
        ---------
            We can override parent class properties and method and change it's value or functionality in child class, as per the requirements.

            <?php
            class Vehicle {
                var $wheelcount = 4;
                var $color = "white";

                function moveWheels() {
                    echo "Vehicle Wheels are moving";
                }
            }

            class Truck extends Vehicle {

                var $wheelcount = 10; //Overriden Vehicle class wheelcount as truck has 10 wheels requirement.

                function moveWheels() {
                    echo "Truck Wheels are moving";
                }
            }

            $truckObject = new Truck();

            echo $truckObject->wheelcount; //* This will print 10. 

            $truckObject->moveWheels(); // this will execute Truck class moveWheels() method.

        ?>

        OverLoading in PHP
        ----------------------
            PHP deoes not support method OverLoading. We can not write another method with same name and different Number
                of argument.

            Constructor also can not be overloaded in PHP. We can write only one constructor(no agrgumnet / with argument ) inside a class.

    Acess Modifiers
    ------------------------
         There are 3 types of access modifiers in PHP which can be applied on properties only, not on functions
            1.public 
            2.protected
            3.private
            4.static

            Security order= public < protected < private

        ex-
            public $wheels= 4;
            private $color = "white";
            protected $ name ="BMW";

            ** var $wheels =4; is same as public $wheels. 

        -> public data can be accessed any where, in any file of our program, even outside the class body.
        -> protected data can be accessed from the same class body and from it's child classes body. Outside the class or child class body it can not be accessible.
        -> private data can be accessed from the same class body only.

        * The data which can not be accesed from OutSide of the class should be managed inside a function of the class and 
            then that function could be called outside the class in order to access the data.  

        Ex-
            <?php
                class Car {
                    public $wheels= 4;
                    protected $ name ="BMW";
                    private $color = "white";
                }

                $bmw = new Car();

                echo $bmw->wheels; // O/P will be 4
                echo $bmw -> name; // ERROR will occur. Bcoz we can't access private data from outside of the class.
            ?>
        To access the protected data from outside of the class, we can make use of a function.
        Ex-
            <?php
                class Car {
                    public $wheels= 4;
                    protected $ name ="BMW";
                    private $color = "white";

                    function showData(){
                        echo $this->name
                    }
                }

                $bmw = new Car();

                echo $bmw->wheels; // O/P will be 4
                echo $bmw -> color;  // ERROR will occured. Bcoz we can't access private data from outside of the class.

                $bmw ->showData(); // This is how we can access protected data from outside of the class body.
            ?>

        static modifier
        -----------------
            Property of a class can be static.
            static properties are class level properties ans we can not access that using object reference.
            It can only be accessed by using class name and "::" notation.

            Ex-
                <?php
                    class Car {
                        static $wheels= 4;

                        function showData() {
                            Car::$wheels = 10;
                        }
                    }

                    $bmw = new Car();
                    echo $bmw->wheels;   // This will give ERROR, as we can't access static data by object reference
                    echo Car :: $wheel;  // This is correct syntax. Should be accessed using class name.
                ?>


Folders and Files
==============================
    Open a existing file or Create new File
    ---------------------
        For File handling there is a function in PHP called fopen('','') which open a stream and by using this stream we can read or write data to the file.
        It has two parameters, Give the File Name with path in 1st arg and in 2nd arg the access type.
            Access type might be Read('r') or Write('w') or both.
        fopen() return a value which can define the access is permitted or not and it holds the connection stream also.

        We can then close the stream by fclose($stream_reference);

        Ex- 
            $file = 'path/example.txt';
            $handle = fopen($file, 'w');
            fclose($handle);

        This will open example.txt file in browser from path folder, if this file is not present there
        then it will create that file there. (If we open txt file in browser, it will show empty body)

    Write to the File
    --------------------
        We use fwrite('','') to write something in a file.
        1st arg is the opened file_stream name and 2nd arg is the content we want to write to the file.

        if($handle) {
            fwrite($handle, "This is the content...");
            fclose($handle);

            echo "Content is written to the file successfully";
        }
        else {
            echo "This Application is not able to write the file";
        }

        *But this will not add up content in the file if you run it multiple times. This will erase the previous content before writing.

    Read file
    -------------
        fread('','') is the function to read data from a file.
            1st arg --> File opened stream name
            2nd arg --> No of bite you want to read, 10 or 20 or 2000, Each bite here is can hold single character 

        It returns data of characters as equal to the bite we have provided in the 2nd arg of fread().
        We can then store that cintent in a php variable.

        ** If we have to read all the characters from the file, then in 2nd arg of fread() we can write 
            filesize($file) ---> This will return the actual file size.

        NOTE --> During read file operation when we create stream(fopen()), the permission should be 'r',
        If we'll put 'w' there, this will clear all the data from the file.

    Delete File
    ---------------
        unlink('path/file_name.extension'); is the function to delete a file.