PHPBasics
PHPBasics refers to a number of things that
arelikely already second nature to you:
–Syntax
–Operators
–Variables
–Constants
–Control Structures
-
LanguageConstructs and Functions
Magicconstants
__LINE__ The current linenumber of the file.
__FILE__ The full path andfilename of the file. If used inside an include, the name of theincluded file is returned. Since PHP 4.0.2, __FILE__always contains an absolute path whereas in older versions itcontained relative path under some circumstances.
__FUNCTION__ The function name.(Added in PHP 4.3.0) As of PHP 5 this constant returns the functionname as it was declared (case-sensitive). In PHP 4 its value isalways lowercased.
__CLASS__ The class name. (Addedin PHP 4.3.0) As of PHP 5 this constant returns the class name as itwas declared (case-sensitive). In PHP 4 its value is alwayslowercased.
__METHOD__ The class method name.(Added in PHP 5.0.0) The method name is returned as it was declared(case-sensitive).
PHPlanguage construct
The "exact" definition for "LanguageConstruct".
It's kind of like the "core languagedefinition" of things such as: if (...) while (...) <?php and?> and so on In PHP, a handful of common things that manybeginners *THINK* are functions are actually Language Constructs:require include echo isset I belive most of them are documented assuch in the manual now. Language Construct roughly corresponds to the"grammar" of the language, if you will.
Thismeans that they are integral part of the language, just like 'if', orany operator +, *, etc, though they look pretty much like functions.It means that though syntactically they look a functions and in themanual they are listed under functions, this is only to make themeasy to use, understand and locate in the documentation. That is whycertain rules for functions can be relaxed, such as requiringparenthesis around its arguments, which are not actually needed butare there so that they have the same look as regular functions.
PHP Tags
Long tags: <?php … ?>
Script syle tags:
<script language = “php”> …</script>
Short tags: short_open_tag directive inphp.ini
<? …?> (<? echo $vars ?>;<?= $vars ?>)
ASP style tags: asp_tags directive inphp.ini
<% … %> (<% echo $vars %>;<%= $vars %>)
Except the long tags, other tags are notpreferred.
Exam questions:
.When you should not use short tags? When usephp with XML.
What kind of errors occurred due to the “shorttags” problem?
A. output javascript source code;
B. Parse error: syntax error,unexpected $end in
Use the long or regular PHP tags to ensureyour application will be portable across multiple servers regardlessof configuration options.
Comments
// single line comment
# single line comment
/*
Multi-line comment
*/
.PHPdoc comment style
Single line comments are ended by either thenewline character or a closing PHP tag, so a single like comment like
//This tag ?> can end PHP code
Can have unintended output
Variables
PHPis loosely typed.
Scalar:Boolean, string, integer, float
Compound:array, object
Special:resource, null
ScalarTypes
Strings
Natively within PHP each character is represented by asingle byte, as such PHP has no native support for multi-bytecharacter sets (like Unicode)
-
This changeswith PHP6.
There is no PHP imposed limit on the length of the strings youcan use.
‘’ The single quote or string literal, characters within singlequotes will be recorded as is, without variable or escape sequencesinterpreted and replaced.
“” The double quotes, variables and escape sequnces will beinterpreted and replaced
<<<– Heredoc
Theheredoc syntax functions in a similar manner to double quotes, but isdesigned to span multiple lines, and allow for the use of quoteswithout escaping.
$greeting= <<<GREETING
Shesaid "That is $name's" dog!
Whilerunning towards the thief
GREETING;
Also,the identifier used must follow the same naming rules as any otherlabel in PHP: it must contain only alphanumeric characters andunderscores, and must start with a non-digit character or underscore.
Itis very important to note that the line with the closing identifiercontains no other characters, except possibly a semicolon (;). Thatmeans especially that the identifier may not be indented, and theremay not be any spaces or tabs after or before the semicolon. It'salso important to realize that the first character before the closingidentifier must be a newline as defined by your operating system.This is \r on Macintosh for example. Closing delimiter (possiblyfollowed by a semicolon) must be followed by a newline too.
Itis not allowed to use heredoc syntax in initializing class members.Use other string syntaxes instead.
Integer
0
0x
Maximum size of an integer is platformdependent, a maximum of ~2Billion is common.
Float (double)
Floats, or doubles, can be used to representreally
large or really small values. Floats can beentered
via several syntaxes
$a = 1.234; //Standard decimal notation
$b = 1.2e3; //Scientific notation (1200)
$c = 7E-10;
//Scientific notation (0.0000000007)
The size of a float is platform-dependent,although a
maximum of ~1.8e308 with a precision
I encountered a questions on the numbernotation conversion. But is relative easy. By default, php is outdecimal numbers.
Boolean
True, false, 0, 1… case-insensitive
CompoundTypes
Arrays
Arrays cancontain any combination of other variable types, even arrays orobjects.
More details onlater lectures.
Objects
Objects allowdata and methods to be combined into one cohesive structure.
More details onlater lectures.
SpecialTypes
Resource
Aresource is a special variable that represents some sort of operatingsystem resource, generally an open file or database connection.
Whilevariables of the type resource can be printed out, their onlysensible use is with the functions designed to work with them.
Null
Anull variable is special in that it has no value and no type.
Nullis not the same as the integer zero or an zero length string (whichwould have types)
Constants
Constants allowyou to create a special identifier that can not be changed oncecreated, this is done using the define() function. Constants can notbe changed once set.
define('username','bob');
VariableVariables
Variable Variables are bothuseful and confusing:
$a= 'name';
$$a= "Paul";
echo$name; //Paul
There are several situationsin which Variable
Variablescan be useful, but use them with care as
theycan easily confuse other programmers.
Operators
PHP supports a multitude of Operators:
–Assignment
–Logical
–Arithmetic
–String
–Comparison
–Bitwise
–Other
.AssignmentBy Value vs By Reference
PassObjects argument in PHP5.
UsingBitwise Operations: &(and), |(or), ^(XOR), ~(NOT)
>>(ShiftRight), <<(Shift Left), paddingwith 0s.
Whatis the output of:
– 1& 2
– 2& 7
– 15& 24
– 1| 2
– 16| 15
– 8^ 6
– 15^ 7
Whatis the output of (within the context of
our8 bit binary world):
–~254
– 4>> 2
– 1<< 2
– 5>> 2
–7<< 3
OtherOperators
@:Suppresses errors from the following expression
``backticks:Execute the contents as a shell command
(shortcutfor shell_exec()).
Instanceof:Returns true if the indicated variable is an instance of thedesignated class, one of it’s subclasses or a designated interface.
Instanceofis somewhat important, cause I encounter some exam questionsregarding this.
ini_set("ERROR_LEVEL",E_STRICT);
$a= @myFunction();
functionmyFunction($a)
{
array_merge(array(),"");
}
$ls= `ls`;
$a= new stdClass;
if($a instanceof stdClass) { ... }
if($a !instanceof stdClass) { ... }
//ParseError
ControlStructures
If
–Alternate * code morereadable.
–Short ($express)?$var1:$var2
Switch
While
do
For
–Continue
–break
Foreach
Functions
–Paramaters
Optional
Byref
Byval
Objects
Variable functions
Objects
-
Later!
if,while, do, for, foreach can have alternate syntax, replace the { and} with : and end(if, while, do etc). Check some WordPress theme filefor real world example.
$a= 0;
while($a++ < 10)
{
echo$a;
}
echo$a;
return
Returnends execution and returns control to the calling scope, functionsboth inside an included file (returning control to the calling file)and from inside a function/method (returning control to the callingcode).
Exit
Haltexecution of the script, can optionally return a message, or an exitstatus (0-255).
Arare exam questions:
End ascript in PHP5:
__halt_compiler() ;
die();
exit();
Conclusion
PHP Tags, multiple types withdifferent use rules (which ones are on/off by default, which ones aguaranteed?)
PHP is loosely typed, but there istyping going onunderneath the hood
Some assumptions are made (octalformat)
Binary is a pain in the neck, but ithas its
uses
Control structures have formats otherthan
theones commonly uses
PHPFunctions
–Readability
–Maintainability
–Code separation
–Modularity
Functions– Scope
Ithink this should expanded to cover the features related to variablescope: Super Global, global variable, local variables, classmembers(public, private, protect, final etc), constant, static etc.
ButPHP free memory on the end of every page load, so even staticvariable can across separate http request; that’s why we needcookies and sessions.
global $id;
globals[‘id’];
Theexam has several questions will need you to clearly understand theFunction Scope. And pass value Byref and Byval.
variable-lengthargument lists
Youcan use variable-length argument lists even if you do specifyarguments in the
functionheader.
func_get_args,func_num_args, func_get_arg
Functions& Objects, Friends at last
InPHP4 Objects were thrown around ByVal,this meant that you made copies without
eventhinking about it.
InPHP5 Objects are always passed ByRefunless you explicitly clone it, keep that in
Mind.
Conclusion
They’reterribly useful
You have to remember how scope works
–Practice tracing
Objects fly around by reference now
Return statements can exist anywherewithin thefunction, you can even have several
Avoid situations where the samefunction mayreturn nothing, or something (Zend
Studio’sCode Analyzer tests for this)
Whathappens if a function is defined then the PHP scope ends, thenresumes again later with the remainder of the function.
Is“_” a valid function name?
PHPArrays
EnumeratedArrays, Associative Arrays (hashes), Multi Dimensional Arrays
$a =array(5=>"b", 7, 9, "23" => 'c', 'j');
$b= array(1, 2, 3, 'f', 'fred' => $a);
How do I access thevalue:
– 7 // $a[6];
– ‘c’ // $a["23"];
– ‘b’ through the array $b // $b['fred'][5]
– ‘f’ // $b[3]
ArrayIteration:
Wheniterating through an array via foreach() keep in mind it operates ona copy of the array.
Usingthe internal array pointer doesn’t have this problem.
ArrayIteration
end() – Move pointer tolast element
key() - Retreives keyfrom current position
next() – Advances arraypointer one spot then
returnscurrent value
prev() – Rewinds thearray pointer one spot, then
returnsthe current value
reset() – Resets thearray pointer to the beginning of
thearray
each() – Returns the
Internalarray pointers can be reset, but don’t reset on their own.
Foreach()
InPHP 5 items can be iterated over by reference rather than simply byvalue.
foreach($arrayAS &$value) { … }
Thisis likely will be examed!
SomeArray functions:
.sort()
Thisfunction sorts an array. Elements will be arranged from lowest tohighest when this function has completed.
This function assignsnew keys for the elements in array. It will remove any existing keysyou may have assigned, rather than just reordering thekeys.
.Ksort()
Sorts an array by key, maintaining key todata correlations. This is useful mainly for associativearrays.
.asort()
Sort an array and maintain indexassociation
array_push() array_unshift()
array_pop() array_shift()
Inassociative arrays strings are used to key the data, keys containingonly digits are cast to integers.
array_keys() &array_values()
bool array_walk ( array &$array, callback$funcname [, mixed $userdata] )
Applies the user-defined functionfuncname to each element of the array array. Typically, funcnametakes on two parameters. The array parameter's value being the first,and the key/index second. If the optional userdata parameter issupplied, it will be passed as the third parameter to the callbackfuncname.
array_change_key_case()
Returns an array withall keys from input lowercased or uppercased. Numbered indices areleft as is.
array_merge()
You can merge arrays usingarray_merge(), when different associative arrays have duplicate keys,the values in the rightmost array takeprecedence.
array_splice()
Cut out a chunk of anarray
array_merge_recursive()
merges the elements of one ormore arrays together so that the values of one are appended to theend of the previous one. It returns the resulting array.
Ifthe input arrays have the same string keys, then the values for thesekeys are merged together into an array, and this is done recursively,so that if one of the values is an array itself, the function willmerge it with a corresponding entry in another array too. If,however, the arrays have the same numeric key, the later value willnot overwrite the original value, but will be appended.