Computer Tutorials: September 2015

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PHP INTRODUCTION

PHP started out as a small open source project that evolved as more and more people found out how useful it was. Rasmus Lerdorf unleashed the first version of PHP way back in 1994.

PHP is a recursive acronym for "PHP: Hypertext Preprocessor".

PHP is a server side scripting language that is embedded in HTML. It is used to manage dynamic content, databases, session tracking, even build entire e-commerce sites.

It is integrated with a number of popular databases, including MySQL, PostgreSQL, Oracle, Sybase, Informix, and Microsoft SQL Server.

PHP is pleasingly zippy in its execution, especially when compiled as an Apache module on the Unix side. The MySQL server, once started, executes even very complex queries with huge result sets in record-setting time.

PHP supports a large number of major protocols such as POP3, IMAP, and LDAP. PHP4 added support for Java and distributed object architectures (COM and CORBA), making n-tier development a possibility for the first time.

PHP is forgiving: PHP language tries to be as forgiving as possible.

PHP Syntax is C-Like.

Common uses of PHP

PHP performs system functions, i.e. from files on a system it can create, open, read, write, and close them.

PHP can handle forms, i.e. gather data from files, save data to a file, thru email you can send data, return data to the user.

You add, delete, modify elements within your database thru PHP.

Access cookies variables and set cookies.

Using PHP, you can restrict users to access some pages of your website.

It can encrypt data.

Characteristics of PHP

Five important characteristics make PHP's practical nature possible −

Simplicity

Efficiency

Security

Flexibility

Familiarity

"Hello World" Script in PHP

To get a feel for PHP, first start with simple PHP scripts. Since "Hello, World!" is an essential example, first we will create a friendly little "Hello, World!" script.

As mentioned earlier, PHP is embedded in HTML. That means that in amongst your normal HTML (or XHTML if you're cutting-edge) you'll have PHP statements like this −

<html>

<head>

<title>Hello World</title>

</head>

<body>

<?php echo "Hello, World!";?>

</body>

</html>

It will produce following result −

Hello, World!

If you examine the HTML output of the above example, you'll notice that the PHP code is not present in the file sent from the server to your Web browser. All of the PHP present in the Web page is processed and stripped from the page; the only thing returned to the client from the Web server is pure HTML output.

All PHP code must be included inside one of the three special markup tags ate are recognised by the PHP Parser.

<?php PHP code goes here ?>

<? PHP code goes here ?>

A most common tag is the <?php...?> and we will also use the same tag in our tutorial.

From the next chapter we will start with PHP Environment Setup on your machine and then we will dig out almost all concepts related to PHP to make you comfortable with the PHP language.

The main way to store information in the middle of a PHP program is by using a variable.

Here are the most important things to know about variables in PHP.

All variables in PHP are denoted with a leading dollar sign ($).

The value of a variable is the value of its most recent assignment.

Variables are assigned with the = operator, with the variable on the left-hand side and the expression to be evaluated on the right.

Variables can, but do not need, to be declared before assignment.

Variables in PHP do not have intrinsic types - a variable does not know in advance whether it will be used to store a number or a string of characters.

Variables used before they are assigned have default values.

PHP does a good job of automatically converting types from one to another when necessary.

PHP variables are Perl-like.

PHP has a total of eight data types which we use to construct our variables −

Integers − are whole numbers, without a decimal point, like 4195.

Doubles − are floating-point numbers, like 3.14159 or 49.1.

Booleans − have only two possible values either true or false.

NULL − is a special type that only has one value: NULL.

Strings − are sequences of characters, like 'PHP supports string operations.'

Arrays − are named and indexed collections of other values.

Objects − are instances of programmer-defined classes, which can package up both other kinds of values and functions that are specific to the class.

Resources − are special variables that hold references to resources external to PHP (such as database connections).

The first five are simple types, and the next two (arrays and objects) are compound - the compound types can package up other arbitrary values of arbitrary type, whereas the simple types cannot.

We will explain only simple data type in this chapters. Array and Objects will be explained separately.

Integers

They are whole numbers, without a decimal point, like 4195. They are the simplest type .they correspond to simple whole numbers, both positive and negative. Integers can be assigned to variables, or they can be used in expressions, like so −

$int_var = 12345;

$another_int = -12345 + 12345;

Integer can be in decimal (base 10), octal (base 8), and hexadecimal (base 16) format. Decimal format is the default, octal integers are specified with a leading 0, and hexadecimals have a leading 0x.

For most common platforms, the largest integer is (2**31 . 1) (or 2,147,483,647), and the smallest (most negative) integer is . (2**31 . 1) (or .2,147,483,647).

Doubles

They like 3.14159 or 49.1. By default, doubles print with the minimum number of decimal places needed. For example, the code −

<?php

$many = 2.2888800;

$many_2 = 2.2111200;

$few = $many + $many_2;

print("$many + $many_2 = $few ");

It produces the following browser output −

2.28888 + 2.21112 = 4.5

Boolean

They have only two possible values either true or false. PHP provides a couple of constants especially for use as Booleans: TRUE and FALSE, which can be used like so −

if (TRUE)

print("This will always print ");

else

print("This will never print ");

Interpreting other types as Booleans

Here are the rules for determine the "truth" of any value not already of the Boolean type −

If the value is a number, it is false if exactly equal to zero and true otherwise.

If the value is a string, it is false if the string is empty (has zero characters) or is the string "0", and is true otherwise.

Values of type NULL are always false.

If the value is an array, it is false if it contains no other values, and it is true otherwise. For an object, containing a value means having a member variable that has been assigned a value.

Valid resources are true (although some functions that return resources when they are successful will return FALSE when unsuccessful).

Don't use double as Booleans.

Each of the following variables has the truth value embedded in its name when it is used in a Boolean context.

$true_num = 3 + 0.14159;

$true_str = "Tried and true"

$true_array[49] = "An array element";

$false_array = array();

$false_null = NULL;

$false_num = 999 - 999;

$false_str = "";

NULL

NULL is a special type that only has one value: NULL. To give a variable the NULL value, simply assign it like this −

$my_var = NULL;

The special constant NULL is capitalized by convention, but actually it is case insensitive; you could just as well have typed −

$my_var = null;

A variable that has been assigned NULL has the following properties −

It evaluates to FALSE in a Boolean context.

It returns FALSE when tested with IsSet() function.

Strings

They are sequences of characters, like "PHP supports string operations". Following are valid examples of string

$string_1 = "This is a string in double quotes";

$string_2 = "This is a somewhat longer, singly quoted string";

$string_39 = "This string has thirty-nine characters";

$string_0 = ""; // a string with zero characters

Singly quoted strings are treated almost literally, whereas doubly quoted strings replace variables with their values as well as specially interpreting certain character sequences.

<?php

$variable = "name";

$literally = 'My $variable will not print!';

print($literally);

print " ";

$literally = "My $variable will print!";

print($literally);

This will produce following result −

My $variable will not print!\n

My name will print

There are no artificial limits on string length - within the bounds of available memory, you ought to be able to make arbitrarily long strings.

Strings that are delimited by double quotes (as in "this") are preprocessed in both the following two ways by PHP −

Certain character sequences beginning with backslash (\) are replaced with special characters

Variable names (starting with $) are replaced with string representations of their values.

The escape-sequence replacements are −

\n is replaced by the newline character

\r is replaced by the carriage-return character

\t is replaced by the tab character

\$ is replaced by the dollar sign itself ($)

\" is replaced by a single double-quote (")

\\ is replaced by a single backslash (\)

Here Document

You can assign multiple lines to a single string variable using here document −

<?php

$channel =<<<_XML_

<title>What's For Dinner</title>

<description>Choose what to eat tonight.</description>

</channel>

_XML_;

echo <<<END

This uses the "here document" syntax to output

multiple lines with variable interpolation. Note

that the here document terminator must appear on a

line with just a semicolon. no extra whitespace!

END;

print $channel;

This will produce following result −

This uses the "here document" syntax to output

multiple lines with variable interpolation. Note

that the here document terminator must appear on a

line with just a semicolon. no extra whitespace!

<title>What's For Dinner<title>

<description>Choose what to eat tonight.</description>

Variable Scope

Scope can be defined as the range of availability a variable has to the program in which it is declared. PHP variables can be one of four scope types −

Local variables

Function parameters

Global variables

Static variables

Variable Naming

Rules for naming a variable is −

Variable names must begin with a letter or underscore character.

A variable name can consist of numbers, letters, underscores but you cannot use characters like + , - , % , ( , ) . & , etc

There is no size limit for variables.

A constant is a name or an identifier for a simple value. A constant value cannot change during the execution of the script. By default, a constant is case-sensitive. By convention, constant identifiers are always uppercase. A constant name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. If you have defined a constant, it can never be changed or undefined.

To define a constant you have to use define() function and to retrieve the value of a constant, you have to simply specifying its name. Unlike with variables, you do not need to have a constant with a $. You can also use the function constant() to read a constant's value if you wish to obtain the constant's name dynamically.

constant() function

As indicated by the name, this function will return the value of the constant.

This is useful when you want to retrieve value of a constant, but you do not know its name, i.e. It is stored in a variable or returned by a function.

constant() example

<?php

define("MINSIZE", 50);

echo MINSIZE;

echo constant("MINSIZE"); // same thing as the previous line

Only scalar data (boolean, integer, float and string) can be contained in constants.

Differences between constants and variables are

There is no need to write a dollar sign ($) before a constant, where as in Variable one has to write a dollar sign.

Constants cannot be defined by simple assignment, they may only be defined using the define() function.

Constants may be defined and accessed anywhere without regard to variable scoping rules.

Once the Constants have been set, may not be redefined or undefined.

Valid and invalid constant names

// Valid constant names

define("ONE", "first thing");

define("TWO2", "second thing");

define("THREE_3", "third thing")

// Invalid constant names

define("2TWO", "second thing");

define("__THREE__", "third value");

PHP Magic constants

PHP provides a large number of predefined constants to any script which it runs.

There are five magical constants that change depending on where they are of __LINE__ depends on the line that it's used on in your script. These special constants are case-insensitive and are as follows −

A few "magical" PHP constants ate given below −

Name	Description
__LINE__	The current line number of the file.
__FILE__	The full path and filename of the file. If used inside an include,the name of the included file is returned. Since PHP 4.0.2, __FILE__ always contains an absolute path whereas in older versions it contained relative path under some circumstances.
__FUNCTION__	The function name. (Added in PHP 4.3.0) As of PHP 5 this constant returns the function name as it was declared (case-sensitive). In PHP 4 its value is always lowercased.
__CLASS__	The class name. (Added in PHP 4.3.0) As of PHP 5 this constant returns the class name as it was declared (case-sensitive). In PHP 4 its value is always lowercased.
__METHOD__	The class method name. (Added in PHP 5.0.0) The method name is returned as it was declared (case-sensitive).

What is Operator? Simple answer can be given using expression 4 + 5 is equal to 9. Here 4 and 5 are called operands and + is called operator. PHP language supports following type of operators.

Arithmetic Operators

Comparison Operators

Logical (or Relational) Operators

Assignment Operators

Conditional (or ternary) Operators

Lets have a look on all operators one by one.

\Arithmetic Operators

There are following arithmetic operators supported by PHP language −

Assume variable A holds 10 and variable B holds 20 then −

Show Examples

Operator	Description	Example
+	Adds two operands	A + B will give 30
-	Subtracts second operand from the first	A - B will give -10
*	Multiply both operands	A * B will give 200
/	Divide numerator by de-numerator	B / A will give 2
%	Modulus Operator and remainder of after an integer division	B % A will give 0
++	Increment operator, increases integer value by one	A++ will give 11
--	Decrement operator, decreases integer value by one	A-- will give 9

Comparison Operators

There are following comparison operators supported by PHP language

Assume variable A holds 10 and variable B holds 20 then −

Show Examples

Operator	Description	Example
==	Checks if the value of two operands are equal or not, if yes then condition becomes true.	(A == B) is not true.
!=	Checks if the value of two operands are equal or not, if values are not equal then condition becomes true.	(A != B) is true.
>	Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true.	(A > B) is not true.
<	Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true.	(A < B) is true.
>=	Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true.	(A >= B) is not true.
<=	Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true.	(A <= B) is true.

Logical Operators

There are following logical operators supported by PHP language

Assume variable A holds 10 and variable B holds 20 then −

Show Examples

Operator	Description	Example
and	Called Logical AND operator. If both the operands are true then condition becomes true.	(A and B) is true.
or	Called Logical OR Operator. If any of the two operands are non zero then condition becomes true.	(A or B) is true.
&&	Called Logical AND operator. If both the operands are non zero then condition becomes true.	(A && B) is true.
\|\|	Called Logical OR Operator. If any of the two operands are non zero then condition becomes true.	(A \|\| B) is true.
!	Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true then Logical NOT operator will make false.	!(A && B) is false.

Assignment Operators

There are following assignment operators supported by PHP language −

Show Examples

Operator	Description	Example
=	Simple assignment operator, Assigns values from right side operands to left side operand	C = A + B will assign value of A + B into C
+=	Add AND assignment operator, It adds right operand to the left operand and assign the result to left operand	C += A is equivalent to C = C + A
-=	Subtract AND assignment operator, It subtracts right operand from the left operand and assign the result to left operand	C -= A is equivalent to C = C - A
*=	Multiply AND assignment operator, It multiplies right operand with the left operand and assign the result to left operand	C = A is equivalent to C = C A
/=	Divide AND assignment operator, It divides left operand with the right operand and assign the result to left operand	C /= A is equivalent to C = C / A
%=	Modulus AND assignment operator, It takes modulus using two operands and assign the result to left operand	C %= A is equivalent to C = C % A

Conditional Operator

There is one more operator called conditional operator. This first evaluates an expression for a true or false value and then execute one of the two given statements depending upon the result of the evaluation. The conditional operator has this syntax −

Show Examples

Operator	Description	Example
? :	Conditional Expression	If Condition is true ? Then value X : Otherwise value Y

Operators Categories

All the operators we have discussed above can be categorised into following categories −

Unary prefix operators, which precede a single operand.

Binary operators, which take two operands and perform a variety of arithmetic and logical operations.

The conditional operator (a ternary operator), which takes three operands and evaluates either the second or third expression, depending on the evaluation of the first expression.

Assignment operators, which assign a value to a variable.

Precedence of PHP Operators

Operator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator −

For example x = 7 + 3 * 2; Here x is assigned 13, not 20 because operator * has higher precedence than + so it first get multiplied with 3*2 and then adds into 7.

Here operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators will be evaluated first.

Category	Operator	Associativity
Unary	! ++ --	Right to left
Multiplicative	* / %	Left to right
Additive	+ -	Left to right
Relational	< <= > >=	Left to right
Equality	== !=	Left to right
Logical AND	&&	Left to right
Logical OR	\|\|	Left to right
Conditional	?:	Right to left
Assignment	= += -= *= /= %=	Right to left

The if, elseif ...else and switch statements are used to take decision based on the different condition.

You can use conditional statements in your code to make your decisions. PHP supports following three decision making statements −

if...else statement − use this statement if you want to execute a set of code when a condition is true and another if the condition is not true

elseif statement − is used with the if...else statement to execute a set of code if one of the several condition is true

switch statement − is used if you want to select one of many blocks of code to be executed, use the Switch statement. The switch statement is used to avoid long blocks of if..elseif..else code.

The If...Else Statement

If you want to execute some code if a condition is true and another code if a condition is false, use the if....else statement.

Syntax

if (condition)

code to be executed if condition is true;

else

code to be executed if condition is false;

Example

The following example will output "Have a nice weekend!" if the current day is Friday, Otherwise, it will output "Have a nice day!":

<html>

<body>

<?php

$d=date("D");

if ($d=="Fri")

echo "Have a nice weekend!";

else

echo "Have a nice day!";

</body>

</html>

It will produce the following result −

The ElseIf Statement

If you want to execute some code if one of the several conditions are true use the elseif statement

Syntax

if (condition)

code to be executed if condition is true;

elseif (condition)

code to be executed if condition is true;

else

code to be executed if condition is false;

Example

The following example will output "Have a nice weekend!" if the current day is Friday, and "Have a nice Sunday!" if the current day is Sunday. Otherwise, it will output "Have a nice day!" −

<html>

<body>

<?php

$d=date("D");

if ($d=="Fri")

echo "Have a nice weekend!";

elseif ($d=="Sun")

echo "Have a nice Sunday!";

else

echo "Have a nice day!";

</body>

</html>

It will produce the following result −

The Switch Statement

If you want to select one of many blocks of code to be executed, use the Switch statement.

The switch statement is used to avoid long blocks of if..elseif..else code.

Syntax

switch (expression)

{

case label1:

code to be executed if expression = label1;

break;

case label2:

code to be executed if expression = label2;

break;

default:

code to be executed

if expression is different

from both label1 and label2;

}

Example

The switch statement works in an unusual way. First it evaluates given expression then seeks a lable to match the resulting value. If a matching value is found then the code associated with the matching label will be executed or if none of the lable matches then statement will execute any specified default code.

<html>

<body>

<?php

$d=date("D");

switch ($d)

{

case "Mon":

echo "Today is Monday";

break;

case "Tue":

echo "Today is Tuesday";

break;

case "Wed":

echo "Today is Wednesday";

break;

case "Thu":

echo "Today is Thursday";

break;

case "Fri":

echo "Today is Friday";

break;

case "Sat":

echo "Today is Saturday";

break;

case "Sun":

echo "Today is Sunday";

break;

default:

echo "Wonder which day is this ?";

}

</body>

</html>

It will produce the following result –

Loops in PHP are used to execute the same block of code a specified number of times. PHP supports following four loop types.

for − loops through a block of code a specified number of times.

while − loops through a block of code if and as long as a specified condition is true.

do...while − loops through a block of code once, and then repeats the loop as long as a special condition is true.

foreach − loops through a block of code for each element in an array.

We will discuss about continue and break keywords used to control the loops execution.

The for loop statement

The for statement is used when you know how many times you want to execute a statement or a block of statements.

Syntax

for (initialization; condition; increment)

{

code to be executed;

}

The initializer is used to set the start value for the counter of the number of loop iterations. A variable may be declared here for this purpose and it is traditional to name it $i.

Example

The following example makes five iterations and changes the assigned value of two variables on each pass of the loop −

<html>

<body>

<?php

$a = 0;

$b = 0;

for( $i=0; $i<5; $i++ )

{

$a += 10;

$b += 5;

}

echo ("At the end of the loop a=$a and b=$b" );

</body>

</html>

This will produce the following result −

At the end of the loop a=50 and b=25

The while loop statement

The while statement will execute a block of code if and as long as a test expression is true.

If the test expression is true then the code block will be executed. After the code has executed the test expression will again be evaluated and the loop will continue until the test expression is found to be false.

Syntax

while (condition)

{

code to be executed;

}

Example

This example decrements a variable value on each iteration of the loop and the counter increments until it reaches 10 when the evaluation is false and the loop ends.

<html>

<body>

<?php

$i = 0;

$num = 50;

while( $i < 10)

{

$num--;

$i++;

}

echo ("Loop stopped at i = $i and num = $num" );

</body>

</html>

This will produce the following result −

Loop stopped at i = 10 and num = 40

The do...while loop statement

The do...while statement will execute a block of code at least once - it then will repeat the loop as long as a condition is true.

Syntax

{

code to be executed;

}

while (condition);

Example

The following example will increment the value of i at least once, and it will continue incrementing the variable i as long as it has a value of less than 10 −

<html>

<body>

<?php

$i = 0;

$num = 0;

do{

$i++;

}

while( $i < 10 );

echo ("Loop stopped at i = $i" );

</body>

</html>

This will produce the following result −

Loop stopped at i = 10

The foreach loop statement

The foreach statement is used to loop through arrays. For each pass the value of the current array element is assigned to $value and the array pointer is moved by one and in the next pass next element will be processed.

Syntax

foreach (array as value)

{

code to be executed;

}

Example

Try out following example to list out the values of an array.

<html>

<body>

<?php

$array = array( 1, 2, 3, 4, 5);

foreach( $array as $value )

{

echo "Value is $value ";

}

</body>

</html>

This will produce the following result −

Value is 1

Value is 2

Value is 3

Value is 4

Value is 5

The break statement

The PHP break keyword is used to terminate the execution of a loop prematurely.

The break statement is situated inside the statement block. If gives you full control and whenever you want to exit from the loop you can come out. After coming out of a loop immediate statement to the loop will be executed.

Example

In the following example condition test becomes true when the counter value reaches 3 and loop terminates.

<html>

<body>

<?php

$i = 0;

while( $i < 10)

{

$i++;

if( $i == 3 )break;

}

echo ("Loop stopped at i = $i" );

</body>

</html>

This will produce the following result −

Loop stopped at i = 3

The continue statement

The PHP continue keyword is used to halt the current iteration of a loop but it does not terminate the loop.

Just like the break statement the continue statement is situated inside the statement block containing the code that the loop executes, preceded by a conditional test. For the pass encountering continue statement, rest of the loop code is skipped and next pass starts.

Example

In the following example loop prints the value of array but for which condition becomes true it just skip the code and next value is printed.

<html>

<body>

<?php

$array = array( 1, 2, 3, 4, 5);

foreach( $array as $value )

{

if( $value == 3 )continue;

echo "Value is $value ";

}

</body>

</html>

This will produce the following result −

Value is 1

Value is 2

Value is 4

Value is 5

PHP - Arrays

An array is a data structure that stores one or more similar type of values in a single value. For example if you want to store 100 numbers then instead of defining 100 variables its easy to define an array of 100 length.

There are three different kind of arrays and each array value is accessed using an ID c which is called array index.

Numeric array − An array with a numeric index. Values are stored and accessed in linear fashion.

Associative array − An array with strings as index. This stores element values in association with key values rather than in a strict linear index order.

Multidimensional array − An array containing one or more arrays and values are accessed using multiple indices

NOTE − Built-in array functions is given in function reference PHP Array Functions

PHP - GET & POST Methods

There are two ways the browser client can send information to the web server.

The GET Method

The POST Method

Before the browser sends the information, it encodes it using a scheme called URL encoding. In this scheme, name/value pairs are joined with equal signs and different pairs are separated by the ampersand.

name1=value1&name2=value2&name3=value3

Spaces are removed and replaced with the + character and any other nonalphanumeric characters are replaced with a hexadecimal values. After the information is encoded it is sent to the server.

The GET Method

The GET method sends the encoded user information appended to the page request. The page and the encoded information are separated by the ?character.

http://www.test.com/index.htm?name1=value1&name2=value2

The GET method produces a long string that appears in your server logs, in the browser's Location: box.

The GET method is restricted to send upto 1024 characters only.

Never use GET method if you have password or other sensitive information to be sent to the server.

GET can't be used to send binary data, like images or word documents, to the server.

The data sent by GET method can be accessed using QUERY_STRING environment variable.

The PHP provides $_GET associative array to access all the sent information using GET method.

PHP - Files & I/O

This chapter will explain following functions related to files −

Opening a file

Reading a file

Writing a file

Closing a file

Opening and Closing Files

The PHP fopen() function is used to open a file. It requires two arguments stating first the file name and then mode in which to operate.

Files modes can be specified as one of the six options in this table.

Mode	Purpose
r	Opens the file for reading only. Places the file pointer at the beginning of the file.
r+	Opens the file for reading and writing. Places the file pointer at the beginning of the file.
w	Opens the file for writing only. Places the file pointer at the beginning of the file. and truncates the file to zero length. If files does not exist then it attempts to create a file.
w+	Opens the file for reading and writing only. Places the file pointer at the beginning of the file. and truncates the file to zero length. If files does not exist then it attempts to create a file.
a	Opens the file for writing only. Places the file pointer at the end of the file. If files does not exist then it attempts to create a file.
a+	Opens the file for reading and writing only. Places the file pointer at the end of the file. If files does not exist then it attempts to create a file.

If an attempt to open a file fails then fopen returns a value of false otherwise it returns a file pointer which is used for further reading or writing to that file.

After making a changes to the opened file it is important to close it with thefclose() function. The fclose() function requires a file pointer as its argument and then returns true when the closure succeeds or false if it fails.

Reading a file

Once a file is opened using fopen() function it can be read with a function called fread(). This function requires two arguments. These must be the file pointer and the length of the file expressed in bytes.

The files length can be found using the filesize() function which takes the file name as its argument and returns the size of the file expressed in bytes.

So here are the steps required to read a file with PHP.

Open a file using fopen() function.

Get the file's length using filesize() function.

Read the file's content using fread() function.

Close the file with fclose() function.

PHP - Functions

PHP functions are similar to other programming languages. A function is a piece of code which takes one more input in the form of parameter and does some processing and returns a value.

You already have seen many functions like fopen() and fread() etc. They are built-in functions but PHP gives you option to create your own functions as well.

There are two parts which should be clear to you −

Creating a PHP Function

Calling a PHP Function

In fact you hardly need to create your own PHP function because there are already more than 1000 of built-in library functions created for different area and you just need to call them according to your requirement.

Please refer to PHP Function Reference for a complete set of useful functions.

Creating PHP Function

Its very easy to create your own PHP function. Suppose you want to create a PHP function which will simply write a simple message on your browser when you will call it. Following example creates a function called writeMessage() and then calls it just after creating it.

Note that while creating a function its name should start with keyword functionand all the PHP code should be put inside { and } braces as shown in the following example below −

<html>

<head>

<title>Writing PHP Function</title>

</head>

<body>

<?php

/* Defining a PHP Function */

function writeMessage()

{

echo "You are really a nice person, Have a nice time!";

}

/* Calling a PHP Function */

writeMessage();

</body>

</html>

This will display following result −

You are really a nice person, Have a nice time!

PHP Functions with Parameters

PHP gives you option to pass your parameters inside a function. You can pass as many as parameters your like. These parameters work like variables inside your function. Following example takes two integer parameters and add them together and then print them.

<html>

<head>

<title>Writing PHP Function with Parameters</title>

</head>

<body>

<?php

function addFunction($num1, $num2)

{

$sum = $num1 + $num2;

echo "Sum of the two numbers is : $sum";

}

addFunction(10, 20);

</body>

</html>

This will display following result −

Sum of the two numbers is : 30

Passing Arguments by Reference

It is possible to pass arguments to functions by reference. This means that a reference to the variable is manipulated by the function rather than a copy of the variable's value.

Any changes made to an argument in these cases will change the value of the original variable. You can pass an argument by reference by adding an ampersand to the variable name in either the function call or the function definition.

Following example depicts both the cases.

<html>

<head>

<title>Passing Argument by Reference</title>

</head>

<body>

<?php

function addFive($num)

{

$num += 5;

}

function addSix(&$num)

{

$num += 6;

}

$orignum = 10;

addFive( $orignum );

echo "Original Value is $orignum ";

addSix( $orignum );

echo "Original Value is $orignum ";

</body>

</html>

This will display following result −

Original Value is 10

Original Value is 16

PHP Functions returning value

A function can return a value using the return statement in conjunction with a value or object. return stops the execution of the function and sends the value back to the calling code.

You can return more than one value from a function using return array(1,2,3,4).

Following example takes two integer parameters and add them together and then returns their sum to the calling program. Note that return keyword is used to return a value from a function.

<html>

<head>

<title>Writing PHP Function which returns value</title>

</head>

<body>

<?php

function addFunction($num1, $num2)

{

$sum = $num1 + $num2;

return $sum;

}

$return_value = addFunction(10, 20);

echo "Returned value from the function : $return_value";

</body>

</html>

This will display following result −

Returned value from the function : 30

Setting Default Values for Function Parameters

You can set a parameter to have a default value if the function's caller doesn't pass it.

Following function prints NULL in case use does not pass any value to this function.

<html>

<head>

<title>Writing PHP Function which returns value</title>

</head>

<body>

<?php

function printMe($param = NULL)

{

print $param;

}

printMe("This is test");

printMe();

</body>

</html>

This will produce following result −

This is test

Dynamic Function Calls

It is possible to assign function names as strings to variables and then treat these variables exactly as you would the function name itself. Following example depicts this behaviour.

<html>

<head>

<title>Dynamic Function Calls</title>

</head>

<body>

<?php

function sayHello()

{

echo "Hello ";

}

$function_holder = "sayHello";

$function_holder();

</body>

</html>

This will display following result −

Hello

PHP - Cookies

Cookies are text files stored on the client computer and they are kept of use tracking purpose. PHP transparently supports HTTP cookies.

There are three steps involved in identifying returning users −

Server script sends a set of cookies to the browser. For example name, age, or identification number etc.

Browser stores this information on local machine for future use.

When next time browser sends any request to web server then it sends those cookies information to the server and server uses that information to identify the user.

PHP - Sessions

An alternative way to make data accessible across the various pages of an entire website is to use a PHP Session.

A session creates a file in a temporary directory on the server where registered session variables and their values are stored. This data will be available to all pages on the site during that visit.

The location of the temporary file is determined by a setting in the php.ini file called session.save_path. Bore using any session variable make sure you have setup this path.

When a session is started following things happen −

PHP first creates a unique identifier for that particular session which is a random string of 32 hexadecimal numbers such as 3c7foj34c3jj973hjkop2fc937e3443.

A cookie called PHPSESSID is automatically sent to the user's computer to store unique session identification string.

A file is automatically created on the server in the designated temporary directory and bears the name of the unique identifier prefixed by sess_ ie sess_3c7foj34c3jj973hjkop2fc937e3443.

When a PHP script wants to retrieve the value from a session variable, PHP automatically gets the unique session identifier string from the PHPSESSID cookie and then looks in its temporary directory for the file bearing that name and a validation can be done by comparing both values.

A session ends when the user loses the browser or after leaving the site, the server will terminate the session after a predetermined period of time, commonly 30 minutes duration.

Starting a PHP Session

A PHP session is easily started by making a call to the session_start()function.This function first checks if a session is already started and if none is started then it starts one. It is recommended to put the call tosession_start() at the beginning of the page.

Session variables are stored in associative array called $_SESSION[]. These variables can be accessed during lifetime of a session.

The following example starts a session then register a variable called counterthat is incremented each time the page is visited during the session.

Make use of isset() function to check if session variable is already set or not.

Put this code in a test.php file and load this file many times to see the result −

<?php

session_start();

if( isset( $_SESSION['counter'] ) )

{

$_SESSION['counter'] += 1;

}

else

{

$_SESSION['counter'] = 1;

}

$msg = "You have visited this page ". $_SESSION['counter'];

$msg .= "in this session.";

<html>

<head>

<title>Setting up a PHP session</title>

</head>

<body>

<?php echo ( $msg ); ?>

</body>

</html>

It will produce the following result −

Destroying a PHP Session

A PHP session can be destroyed by session_destroy() function. This function does not need any argument and a single call can destroy all the session variables. If you want to destroy a single session variable then you can useunset() function to unset a session variable.

Here is the example to unset a single variable −

<?php

unset($_SESSION['counter']);

Here is the call which will destroy all the session variables −

<?php

session_destroy();

Turning on Auto Session

You don't need to call start_session() function to start a session when a user visits your site if you can set session.auto_start variable to 1 in php.ini file.

Sessions without cookies

There may be a case when a user does not allow to store cookies on their machine. So there is another method to send session ID to the browser.

Alternatively, you can use the constant SID which is defined if the session started. If the client did not send an appropriate session cookie, it has the form session_name=session_id. Otherwise, it expands to an empty string. Thus, you can embed it unconditionally into URLs.

The following example demonstrates how to register a variable, and how to link correctly to another page using SID.

<?php

session_start();

if (isset($_SESSION['counter'])) {

$_SESSION['counter'] = 1;

}

else {

$_SESSION['counter']++;

}

$msg = "You have visited this page ". $_SESSION['counter'];

$msg .= "in this session.";

echo ( $msg );

To continue click following link

It will produce the following result −

The htmlspecialchars() may be used when printing the SID in order to prevent XSS related attacks.

Saturday, 26 September 2015

PHP Scripting Language