PHP

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PHP

• Server-side Programming

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PHP

• PHP stands for PHP Hypertext Preprocessor
• Originally Personal Home Page
• PHP is interpreted
• PHP code is embedded into HTML code
• interpreter is invoked by the web server
• Syntax is similar to C, Java, Perl etc.
• Think of a cross between perl and C
• PHP is open source, free, available for most
  platforms, popular

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What can you do with PHP

• Generate content as an HTML page is loaded
  (generate HTML code)
• User sees only the generated code, not your PHP
  code
• Respond to a form with dynamic content
• Retrieve and display information from a database
  or server-side files

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Where does the PHP code go?

• PHP code goes into a special element type in your
  HTML files.
• lt?php ?gt
• You can have multiple php elements in a page
• Code in the php element is sent to the php
  interpreter everything else is assumed to be
  content
• File needs to have a .php or .phtml extension

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HelloWorld in PHP

• lthtmlgt
• ltheadgt
• lttitlegtPHPlt/titlegt
• lt/headgt
• ltbodygt
• lt?php echo 'Hello, world!' ?gt
• lt/bodygt
• lt/htmlgt

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Basics

• Syntax is similar to C and perl
• Comments
• //
• / /
• Statements are terminated by semicolon
• is compound statement, not a block
• Whitespace insensitive
• Reserved words, function names are
  case-insensitive

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More Basics

• Variable names (case-sensitive) same as for Java
  with a in front
• can be assigned by value or by reference
• Dynamically typed
• For output use
• echo
• print
• printf just like in C

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Here Documents

• Instead of using multiple print statements, use a
  here document
• print ltltlt_HTML_
• lthtmlgtltheadgt lt/headgt
• ltbodygt lt/bodygtlt/htmlgt
• _HTML_
• Everything between the two _HTML_ is printed

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Built-In Types

• Primitive
• boolean
• integer
• float
• string

• Compound
• array (similar to hash in perl)
• object - defined by a class
• Special types
• NULL
• resource

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Strings

• Use either double or single quotes for strings
• In single-quoted strings, all characters are
  interpreted literally
• Variables and escape characters are interpreted
  in double-quoted strings
• Strings can extend over multiple lines

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String functions

• trim removes leading and trailing whitespace
• ltrim and chop remove from one end
• strlen gives number of characters in the string
• can be used to compare strings (case
  sensitive)
• strcasecmp() compares strings ignoring case
  (semantics of C strcmp)
• Use . for concatenation
• get substrings using substr( string, start,
  length)

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Numbers

• PHP distinguishes between integer and floating
  point values
• Usual set of arithmetic operations and assignment
  operators
• integer division can give floating point result
• coerces operands to integers
• Usual set of mathematical functions
• Other functions for things like formatting, type
  conversion,

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Booleans

• False values are 0, 0.0, "0", "", false, NULL,
  array with 0 elements, object with 0 member
  variables
• everything else is true
• Usual set of comparison operators
• (lt lt ! gt gt)
• work with strings
• Usual set of logical operators (! ) plus and
  or xor

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Type Conversions

• Coercion (automatic type conversion) happens
  based on context. It happens in more ways than in
  Java.
• integer -gt double
• numeric, boolean -gt string
• double -gt integer
• numeric -gt boolean
• string -gt numeric
• Explicit type conversion
• (int)sum
• intval(sum)
• settype(sum, "integer")

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Control Statements

• Selection
• if ( cond)
• elseif (cond2)
• else
• also switch

• Loops
• while (cond)
• do
• while( cond)
• for (init cond update)
• foreach()

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Declaring Functions

• function functionName(paramList)
• / code goes here /
• paramList is comma-separated list of param names
  with optional default values
• parameters with default values need to be at the
  end of the list
• use return to return a value
• functions can be nested in PHP

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Calling Functions

• functionName( argList)
• argList is comma-separated list of expressions
• number of arguments needs to match the number of
  parameters unless default values have been
  assigned
• if the last n parameters have default values, you
  can omit the last 1, 2, .. n arguments
• you can't skip a position in the argument list

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Variable scope

• Variables defined outside of any function are
  global
• Variables defined inside a function are local to
  the function (as are parameters)
• To use global variables in a function
• get them from GLOBALS, an array containing all
  global variables
• x GLOBALS'varname'
• use the global keyword to declare them to be
  global
• global varname

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Compound Types in PHP

• PHP has two compound types
• Arrays -arrays in PHP are really ordered maps
  (hash tables)
• multi-dimensional arrays are arrays whose
  elements are arrays
• Objects - variables whose type is defined by a
  class

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Arrays

• An array consists of a collection of elements
• each element has a key and a value (like a hash
  table)
• arrays with only numeric keys are a special case
• you can use arrays with numeric keys the same way
  you do an array in C or Java

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Creating an array

• Create dynamically by assigning values to
  elements
• veggie'corn' 'yellow'
• dinner0 'Lemon Chicken'
• Use the Array constructor
• veggie array( 'corn' gt 'yellow', 'beet' gt
  'red', 'carrot' gt 'orange')

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Creating a numeric array

• Use array with just a list of values
• keys will automatically be numbers (starting from
  0)
• dinner ('Sweet Corn and Asparagus', 'Lemon
  Chicken', 'Spicy Eggplant')
• Add new elements to end of list by assigning with
  no index
• dinner 'Braised Bamboo fungus'

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Using arrays

• count(arrayName) gives the number of elements in
  the array
• implode(delim, array) creates a string from an
  array
• menu implode( ', ', dinner)
• explode(delim, string) creates a numeric array
  from a string
• dinner explode( ', ', menu)

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Sorting arrays

• The array elements will be rearranged by these
  methods
• sort()/rsort() sort by element values
  (ascending/descending)
• keys become numeric
• asort()/arsort() sort by element value, keeping
  keys and values together
• ksort()/krsort() sort by key, keeping keys and
  values together

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Looping with arrays

• Use foreach to loop through elements of array
• foreach( meal as key gt value)
• print "key value\n"
• foreach( dinner as dish)
• print "You can eat dish.\n"
• foreach goes through elements in order they were
  added to array
• not necessarily numeric order

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Using arrays as lists and stacks

• The functions current, next, prev, reset (which
  take an array parameter) allow you to use an
  array like a linked list.
• list order is the order of insertion
• array_push and array_pop allow you to use an
  array for a stack

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Classes and Objects

• PHP supports object-oriented programming
• Class is a template describing both data and
  operations
• Method is a function defined in a class
• Property is a variable defined in a class
• Constructor is used to create instances (objects)
• Static method doesn't need an object

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Sample Class definition

• class Cart
• var items // Items in our shopping cart
• // Add num articles of artnr to the cart
• function add_item(artnr, num)
• this-gtitemsartnr num
• // Take num articles of artnr out of the cart
• function remove_item(artnr, num)
• if (this-gtitemsartnr gt num)
• this-gtitemsartnr - num
• return true
• elseif (this-gtitemsartnr num)
• unset(this-gtitemsartnr)
• return true
• else return false

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Constructors

• Constructor is a method with the same name as the
  class
• Use it to initialize properties
• class Item
• var catalogNum, price
• function Item(id'none', cost'0.0')
• catalogNumid
• price cost

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Using Objects

• Use new to create objects
• myItem new Item( 'AB234', 3.95)
• Access methods and properties with -gt operator
• charge myItem-gtprice

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Regular Expressions

• PHP has POSIX regular expressions built in
• The PCRE module allows you to use Perl compatible
  regular expressions
• preg_match takes a pattern and a string and
  returns true or false
• preg_split takes a delimiter and a string and
  returns an array

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Running Shell Commands

• PHP provides the shell_exec() function for
  running an external program from the php program
• filelist shell_exec( 'ls')
• If you are passing form input on to another
  program, use escapeshellargs() to clean it up
  first

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Extensions

• The mycrypt extension to PHP provides a number of
  standard encryption algorithms
• The Perl and Java extensions allow you to execute
  code written in those languages from your PHP
  program
• PEAR is an extension that is useful for
  applications that use databases
• more next time

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Sources

• Learning PHP 5 by David Sklar
• Programming the World Wide Web by Robert Sebesta
• Programming PHP by Rasmus Ledorf and Kevin Tatroe
• PHP home page
• http//www.php.net/