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Intro to PHP Intro to PHP • What is PHP? – Language developed by Rasmus Lerdorf from the Apache Group – Its primary use is for server-side scripng • Ex: To process HTML forms • Ex: To perform a DB query and pass on results • Ex: To dynamically generate HTML – PHP scripts are oJen embedded within HTML documents • The server processes the HTML document, execuAng the PHP segments and subsAtuAng the output within the HTML document Lecture 2 1 Intro to PHP – The modified document is then sent to the client – As menAoned previously, the client never sees the PHP code • The only reason the client even knows PHP is involved is due to the file extension à .php • But even this is not required if the server is configured correctly – The server can be configured to run PHP scripts even if the file does not have a .php extension – By default XAMPP will only execute PHP if the .php extension is provided – See what happens if you have PHP code without the .php extension Lecture 2 2 Intro to PHP • PHP is a HUGE language – It is a fully funcAonal language – It has an incredible amount of built-in features • Form processing • Output / generate various types of data (not just text) • Database access – Allows for various DBs and DB formats • Object-oriented features – Somewhat of a loose hybrid of C++ and Java • Huge funcAon / class library Lecture 2 3 Intro to PHP • We will look at only a small part of PHP – There are also many tools that are already pre-wri^en in / for PHP • If you are building a substanAal project you may want to use some of these – Ex: h^p://github.com/pear – Also see h^p://www.php.net/sites.php • There are also content management systems wri^en in PHP – Ex: h^p://drupal.org/ – Ex: hp://wordpress.org/ • However, we may not be covering them here – We will focus on the straight PHP language Lecture 2 4 Intro to PHP • PHP Program Structure – Or really lack thereof – PHP, as with many scripAng languages, does not have nearly the same structural requirements as a language like Java – A script can be just a few lines of code or a very large, structured program with classes and objects • The complexity depends on the task at hand – However, there are some guidelines for incorporang PHP scripts into HTML files Lecture 2 5 Intro to PHP – When a PHP file is requested, the PHP interpreter parses the enAre file • Any content within PHP delimiter tags is interpreted, and the output subsAtuted • Any other content (i.e. not within PHP delimiter tags) is simply passed on unchanged • This allows us to easily mix PHP and other content (ex: HTML) • See: – h^p://us3.php.net/manual/en/language.basic-syntax.phptags.php – h^p://us3.php.net/manual/en/language.basic-syntax.phpmode.php Lecture 2 6 Intro to PHP • Consider the following PHP file HTML 5 Document <!DOCTYPE html> <html> Root HTML Tag <head> <title>Simple PHP Example</title> Document Head </head> <body> D <?php echo "<p><h1>Output</h1>"; O echo "<h2>Output</h2>"; echo "<h3>Output</h3></p>"; PHP Code C ?> <script language="PHP"> B echo "\n<b>More PHP Output</b>\n"; echo "New line in source but not rendered"; O echo "<br/>"; D echo "New line rendered but not in source"; Y </script> </body> </html> Lecture 2 7 Intro. to PHP • Now consider the resulAng HTML <!DOCTYPE html> <html> <head> <title>Simple PHP Example</title> </head> <body> <p><h1>Output</h1><h2>Output</h2><h3>Output</h3></p> <b>More PHP Output</b> New line in source but not rendered<br/> New line rendered but not in source </body> </html> • How will it look in the browser? – Look at it in the browser! – See ex2.php Lecture 2 8 Intro to PHP – If we prefer to separate a PHP code segment from the rest of our script, we can write it in another file and include it • SomeAmes it is easier if we "separate" the PHP code from the straight html – We also may be using several different files, esp. if we are using classes • But we must tag it even if it is already within a PHP tagged segment – Included files are not interpreted by default » Don’t necessarily have to be PHP » If we want PHP, include PHP tags within the included file – See ex3.php – See h^p://us3.php.net/manual/en/funcAon.include.php Lecture 2 9 Lecture 2: Intro to PHP • Simple types • See: h^p://us3.php.net/manual/en/language.types.php – boolean • TRUE or FALSE – integer • Plaorm dependent – size of one machine word – typically 32 or 64 bits – float • Double precision • We could call it a double, but since we don't declare variables (we will discuss shortly) float works Lecture 2 10 Intro to PHP – string • We have single-quoted and double-quoted string literals – Double quoted allows for more escape sequences and allows variables to be interpolated into the string – What does that mean? » Rather than outpung the name of the variable, we output its contents, even within a quote » We'll see an example once we define variables » Note that this is NOT done in Java » See example • Length can be arbitrary – Grows as necessary Lecture 2 11 Intro to PHP • Easy conversion back and forth between strings and numbers – In Web applicaons these are mixed a lot, so PHP will implicitly cast between the types when appropriate – This is another clear difference between PHP and Java » Java requires explicit casAng » PHP allows explicit casAng if desired – See: h^p://us3.php.net/manual/en/language.types.type-juggling.php • Can be indexed – the preferred way is using square brackets $mystring = "hello"; echo $mystring[1]; – Output here is 'e' Lecture 2 12 Intro to PHP • PHP variables – All PHP variables begin with the $ • Variable names can begin with an underscore • Otherwise rules are similar to most other languages – Variables are dynamically typed • No type declaraons – Variables are BOUND or UNBOUND » Unbound variables have the value NULL – Type informaon for a variable is obtained from the current bound value – Compare this to Java Lecture 2 13 Intro to PHP • Java typing discipline: Static, strong, safe, nominave (name), manifest • PHP typing discipline: Dynamic, weak • InvesAgate what these classificaAons mean! Lecture 2 14 Intro to PHP – Implicaons of dynamic typing: • No “type clash” errors like in Java int x = 3.5; // oh no! String s = 100; // argh! – Instead we have in PHP $x = 3.5; // no problem! $s = 100; // a-ok! • A variable’s type may change throughout program execuAon $x = 5; // integer $x = 5 + 4 // integer $x = $x + 1.5; // float $x = $x . “ dollars”; // string Lecture 2 15 Intro to PHP – Perhaps intenAonally but perhaps by mistake – We have to be careful and to test types during execuAon – geype() funcAon returns a string representaon of variable’s type $x = 5; echo(geype($x)); // integer $x = $x + 1.5; echo (geype($x)); // float $x = $x . “ dollars”; echo(geype($x)); // string – is_<type>() funcAon returns a boolean to test for a given <type> $x = 5; $check = is_int($x); // true $check = is_float($x); // false – Can use these tests to make decisions within a script – See ex4.php Lecture 2 16 Intro to PHP – PHP programs have access to a large number of predefined variables • These variables allow the script access to server informaon, form parameters, environment informaon, etc. • Very helpful (as we will see) for determining and maintaining state informaon • Ex: – $_SERVER is an array containing much informaon about the server – $_POST is an array containing variables passed to a script via HTTP POST – $_COOKIE is an array containing cookies – See ex5.php Lecture 2 17 Intro to PHP • PHP Expressions and Operators – Similar to those in C++ / Java / Perl – Be careful with a few operators • / in PHP is always floang point division – To get integer division, we must cast to int $x = 15; $y = 6; echo ($x/$y), (int) ($x/$y), "<BR />"; » Output is 2.5 2 • Mixed operands can produce odd results – Values may be cast before comparing Lecture 2 18 Intro to PHP Consider comparing a string and an int • Any non-numeric PHP string value will “equal” 0 • Any numeric PHP string will equal the number it represents – first few digits Consider comparing a string and a boolean • Regular PHP string value will “equal” true • “0” string will equal false • Consider comparing an int and boolean • 0, 0.0 are false; anything else is true • Consider int and float • Float is changed to an integer Lecture 2 19 Intro to PHP • To compare strings, it is be^er to use the C- like string comparison funcAon, strcmp() • Other string funcAons are listed in Sebesta Table 9.3 • Even the == operator has odd behavior in PHP when operands are mixed Lecture 2 20 Intro to PHP • An addiAonal equality operator and inequality operator are defined === returns true only if the variables have the same value and are of the same type » If casAng occurred to compare, the result is false !== returns true if the operands differ in value or in type – Precedence and associavity are similar to C++/ Java • See h^p://us2.php.net/manual/en/language.operators.precedence.php Lecture 2 21 Intro to PHP • PHP Control Structures – Again, these are similar to those in C++ / Java • if, while, do, for, switch are virtually idenAcal to those in C+ + and Java • PHP allows for an alternave syntax to designate a block in the if, while, for and switch statements – Open the block with : rather than { – Close the block with endif, endwhile, endfor, endswitch » for (expr1; expr2; expr3): statement ..
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