Var statement in php

Var statement in php

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• PHP Tutorial
• PHP | Introduction
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• How to set PHP development environment in windows ?
• LAMP installation and important PHP configurations on Ubuntu
• PHP | Coding Standards
• PHP | Basic Syntax
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• PHP echo and print
• PHP | Data Types
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• PHP | Constants
• PHP | Magic Constants
• PHP | Decision Making
• PHP | Loops
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• PHP Examples

• Describe PHP Include and Require
• PHP | Basics of File Handling
• PHP | fopen( ) (Function open file or URL)
• PHP fread( ) Function
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• PHP | fwrite( ) Function
• PHP | Uploading File
• PHP Cookies
• PHP | Sessions
• PHP Filter and Filter Constant
• Implementing callback in PHP
• Exception Handling in PHP

• PHP | Arrays
• PHP array() Function
• PHP | array_change_key_case() Function
• PHP array_chunk() Function
• PHP | array_column() Function
• PHP array_combine() Function
• PHP array_count_values() Function
• PHP array_diff() function
• PHP array_diff_assoc() Function
• PHP array_diff_key() Function
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• PHP Array Functions Complete Reference

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• PHP | date_create(), date_format(), date_add() Functions
• PHP | date_create_from_format() Function
• PHP | date_date_set() Function
• PHP | date_default_timezone_get() Function
• PHP | date_default_timezone_set() Function
• PHP | date_diff() Function
• PHP | date_get_last_errors() Function
• PHP | date_isodate_set() Function
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• PHP | date_sub() Function

• PHP basename( ) Function
• PHP chgrp( ) Function
• PHP chmod( ) Function
• PHP chown( ) Function
• PHP copy( ) Function
• PHP dirname( ) Function
• PHP disk_free_space( ) Function
• PHP disk_total_space( ) Function
• PHP feof( ) Function
• PHP fflush( ) Function
• PHP | fgetc( ) Function
• PHP | fgets( ) Function
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• PHP file_get_contents() Function
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• PHP | Ds\Map diff() Function
• PHP | Ds\Map filter() Function
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• PHP Ds\Map Functions Complete Reference

• SplDoublyLinkedList in PHP
• PHP SplDoublyLinkedList add() Function
• PHP SplDoublyLinkedList bottom() Function
• PHP SplDoublyLinkedList count() function
• PHP SplFixedArray count() Function
• PHP SplFixedArray current() Function
• PHP SplFixedArray getSize() Function
• PHP SplFixedArray key() Function
• PHP SplObjectStorage addAll() Function
• PHP SplObjectStorage attach() Function
• PHP SplObjectStorage contains() Function
• PHP SplObjectStorage count() Function
• PHP SplQueue::__construct() Function
• PHP SPL Data structures Complete Reference

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Var statement in php

It may be worth specifically noting, if variable names follow some kind of «template,» they can be referenced like this:

// Given these variables .
$nameTypes = array( «first» , «last» , «company» );
$name_first = «John» ;
$name_last = «Doe» ;
$name_company = «PHP.net» ;

// Then this loop is .
foreach( $nameTypes as $type )
print $ < "name_ $type " >. «\n» ;

// . equivalent to this print statement.
print » $name_first \n $name_last \n $name_company \n» ;
?>

This is apparent from the notes others have left, but is not explicitly stated.

In addition, it is possible to use associative array to secure name of variables available to be used within a function (or class / not tested).

This way the variable variable feature is useful to validate variables; define, output and manage only within the function that receives as parameter
an associative array :
array(‘index’=>’value’,’index’=>’value’);
index = reference to variable to be used within function
value = name of the variable to be used within function

$vars = [ ‘id’ => ‘user_id’ , ’email’ => ‘user_email’ ];

function validateVarsFunction ( $vars )

//$vars[‘id’]=34; // define allowed variables
$user_id = 21 ;
$user_email = ’email@mail.com’ ;

echo $vars [ ‘id’ ]; // prints name of variable: user_id
echo $< $vars [ 'id' ]>; // prints 21
echo ‘Email: ‘ .$< $vars [ 'email' ]>; // print email@mail.com

// we don’t have the name of the variables before declaring them inside the function
>
?>

The feature of variable variable names is welcome, but it should be avoided when possible. Modern IDE software fails to interpret such variables correctly, regular find/replace also fails. It’s a kind of magic 🙂 This may really make it hard to refactor code. Imagine you want to rename variable $username to $userName and try to find all occurrences of $username in code by checking «$userName». You may easily omit:
$a = ‘username’;
echo $$a;

If you want to use a variable value in part of the name of a variable variable (not the whole name itself), you can do like the following:

$price_for_monday = 10 ;
$price_for_tuesday = 20 ;
$price_for_wednesday = 30 ;

$price_for_today = $< 'price_for_' . $today >;
echo $price_for_today ; // will return 20
?>

PHP actually supports invoking a new instance of a class using a variable class name since at least version 5.2

class Foo public function hello () echo ‘Hello world!’ ;
>
>
$my_foo = ‘Foo’ ;
$a = new $my_foo ();
$a -> hello (); //prints ‘Hello world!’
?>

Additionally, you can access static methods and properties using variable class names, but only since PHP 5.3

class Foo public static function hello () echo ‘Hello world!’ ;
>
>
$my_foo = ‘Foo’ ;
$my_foo :: hello (); //prints ‘Hello world!’
?>

You may think of using variable variables to dynamically generate variables from an array, by doing something similar to: —

foreach ( $array as $key => $value )
$ $key = $value ;
>

?>

This however would be reinventing the wheel when you can simply use:

extract ( $array , EXTR_OVERWRITE );
?>

Note that this will overwrite the contents of variables that already exist.

Extract has useful functionality to prevent this, or you may group the variables by using prefixes too, so you could use: —

$array =array( «one» => «First Value» ,
«two» => «2nd Value» ,
«three» => «8»
);

extract ( $array , EXTR_PREFIX_ALL , «my_prefix_» );

?>

This would create variables: —
$my_prefix_one
$my_prefix_two
$my_prefix_three

containing: —
«First Value», «2nd Value» and «8» respectively

Another use for this feature in PHP is dynamic parsing..

Due to the rather odd structure of an input string I am currently parsing, I must have a reference for each particular object instantiation in the order which they were created. In addition, because of the syntax of the input string, elements of the previous object creation are required for the current one.

Normally, you won’t need something this convolute. In this example, I needed to load an array with dynamically named objects — (yes, this has some basic Object Oriented programming, please bare with me..)

// this is only a skeletal example, of course.
$object_array = array();

// assume the $input array has tokens for parsing.
foreach ( $input_array as $key => $value ) <
// test to ensure the $value is what we need.
$obj = «obj» . $key ;
$ $obj = new Obj ( $value , $other_var );
Array_Push ( $object_array , $ $obj );
// etc..
>

?>

Now, we can use basic array manipulation to get these objects out in the particular order we need, and the objects no longer are dependant on the previous ones.

I haven’t fully tested the implimentation of the objects. The scope of a variable-variable’s object attributes (get all that?) is a little tough to crack. Regardless, this is another example of the manner in which the var-vars can be used with precision where tedious, extra hard-coding is the only alternative.

Then, we can easily pull everything back out again using a basic array function: foreach.

//.
foreach( $array as $key => $object )

echo $key . » — » . $object -> print_fcn (). »
\n» ;

?>

Through this, we can pull a dynamically named object out of the array it was stored in without actually knowing its name.

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