What is variable variables in php

PHP’s Variable Variables: Understanding Their Purpose

To gain a better understanding of local variables in Php, it is important for programmers to grasp the following key points. Firstly, local variables are defined and utilized solely within a function. Additionally, it should be noted that local variables lack scope beyond the function and therefore cannot be referenced or utilized outside of it.

What’s an actual use of variable variables?

The aim, as I understand it, is to provide a means for inexperienced programmers to modify data dynamically without resorting to complex entities such as composite types, namely arrays and objects.

A variable variable is a type of array that can also be referred to as a map or dictionary.

 1); $bar = 'a'; echo $foo[$bar]."\n"; $foo_a = 1; $bar = 'a'; $vv = "foo_$bar"; echo $$vv."\n"; ?> 

By enclosing your «variable variables» within a parent array, it is possible to eliminate the need for them.

Within classes, I have observed individuals utilizing properties that are variable.

$key)) return $this->$key; > > $foo = new Foo(); echo $foo->a; ?> 

But again, you could use an array:

 1); public function __get($key) < if (array_key_exists($key, $this->props)) return $this->props[$key]; > > $foo = new Foo(); echo $foo->a; ?> 

You are not obligated to utilize variable variables or properties in your written code. If given the choice, I would avoid variable variables altogether. However, I do sometimes use variable properties, yet I tend to opt for arrays when accessing data in that manner.

In one particular instance, I came across a helpful application for it. Specifically, I was working with YouTube API outputs that were structured in JSON format, such as the following.

 $obj->media$title => Video title 

Local Variable in PHP | How does the local variable works in PHP?, Local variables are those variables that are declared inside the function of a Php program and have their scope inside that function only. Local variables have

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Local Variable in PHP

Definition of Local Variable in PHP

In PHP programs, local variables are declared inside a function and only have scope within that function. These variables cannot be referenced outside the function and therefore cannot be used outside of its scope in the program. If a global variable with the same name is used outside of the function, it is considered a different variable with its own identity. Local variables follow the same naming conventions as normal variables, starting with a ‘$’ sign and either a letter (a-z) or an underscore sign (_).

In an oho program, local variables can’t be used without defining them inside a function. There is no specific syntax for using them in the program.

//here var1 is a global variable
$var1= 900;
//php function
function xyz()
<
//here var1 is a local variable
//so can be used inside this function only
$var1 =’abc’;
// some php function code
>
locVar();
// php code
?>

How does the local variable work in Php?

Php has 3 main categories of variables: Local, Global, and Static Variables. These variables differ in terms of their scope and how they are defined in the program. This article will focus on local variables and provide important insights that programmers should understand to have a clear understanding of local variables in Php.

In PHP, local variables are confined to the function where they are declared and cannot be accessed outside of it due to their local scope. It is important to note that global variables with the same name as a local variable within a function are separate entities and do not affect each other. Thus, they should be treated as distinct variables with no relation to each other.

Upon calling the local variable within the function, its value will appear on the console. However, if a PHP program attempts to print or use local variables outside of the function, an error message will be displayed to the user. Similar to regular PHP variables, local variables are denoted with a ‘$’ sign.

Examples

To gain a deeper understanding, it is crucial to execute tasks programmatically. The following examples demonstrate the implementation of local variables in Php programs.

Example #1: Program to print the value of local variable outside the function

//php function
function myLocal() <
// local variable ‘name’ having the local scope
$name = ‘Rajesh’;
echo «

Hello the value of local variable inside the function is : $name

«;
>
//calling the function
myLocal();
// printing the value of local variable outside the function, gives an error
echo «

Value of local variable outside the function is : $name

«;
?>

Explanation:

The function ‘myLocal’ in Php has a local variable called ‘name’ with the value ‘Rajesh’. When the function is called and the value of the local variable is printed on the console, ‘Rajesh’ is displayed. However, outside the function, the variable ‘name’ has local scope and therefore nothing is displayed.

Example #2: Program having the value of both local and Global variables with the same name and different value.

// global variable
$name = ‘Ankita’;
function myLocal() <
$name = ‘Rajesh’; // local variable having the local scope
echo «

Hello the value of local variable inside the function is : $name

«;
>
//calling the function
myLocal();
// printing the value of variable outside the function, will consider the global function
echo «

Value of variable outside the function is : $name

«;
?>

Explanation:

The function named myLocal() has a local variable called ‘name’ with a value of ‘Rajesh’ in the example above. Prior to the myLocal() function, a variable called ‘name’ with a value of ‘Ankita’ is defined at the beginning of the code. When the value of the ‘name’ variable is printed inside the myLocal() function, ‘Rajesh’ is displayed. Conversely, when it is printed outside of the function, ‘Ankita’ is displayed. Despite having the same name, the two variables ‘name’ are unrelated and have no connection to one another.

Example #3: Program having the 2 functions with the same name of variables in both the functions.

//function addition with the 2 local variables ‘value1’ and ‘value2’
function addition()
<
$value1 =95;
$value2 =20;
$addition =$value1 + $value2;
echo »

Result of the above addition : $addition

«;
>
//function subtraction with the 2 local variables ‘value1’ and ‘value2’
function subtraction()
<
$value1 =99;
$value2 =9;
$subtraction =$value1 — $value2;
echo »

Result of the above subtraction : $subtraction

«;
>
//calling the above 2 functions
addition();
subtraction();
// printing the values of the local variables outside the function
echo »

Result of the above addition outside function : $addition

«;
echo »

Result of the above subtraction outside function : $subtraction

«;
?>

Explanation:

The example above utilizes two functions, specifically addition and subtraction, each with their own local variables named ‘value1’ and ‘value2’. The scope of these variables is limited to their respective functions. The functions perform addition and subtraction operations and the results are stored as local variables, ‘addition’ and ‘subtraction’. The output of these local variables is displayed on the console when printed inside their respective functions. However, when printed outside the functions, there is no output displayed to the user.

Conclusion

The above explanation provides a clear understanding of the usage of local variables in a PHP program. It is essential for programmers to grasp this basic concept before delving into more advanced topics. By utilizing local variables in their programs, programmers can gain a deeper understanding of the concepts at hand.

Final thoughts

Discover the world of Local Variables in PHP with our comprehensive guide. Gain insights into their definition, syntax, and functioning in PHP through detailed examples with code implementation. Expand your knowledge by exploring additional articles on related topics.

PHP | Variables, Variables in a program are used to store some values or data that can be used later in a program. The variables are also like containers

Why use dynamic variables (variable variables) in PHP or other languages [duplicate]

Initially, I had cast a vote to close this question due to its subjective nature. However, upon further contemplation, I am now able to provide an objective response.

A name assigned to a static variable is a string of characters that serves as a label recognized by the underlying engine to associate with the value represented by the variable. This is a simplified explanation for non-technical individuals.

A string is referred to as a «sequence of characters». It is an expression used to represent a string. Therefore, any expression that represents a string can be used to represent a variable token. This expression can also be assigned to a variable, resulting in dynamic variable names.

However, your inquiry was not about that. Your query was focused on the reason behind it.

Implementors of a language are not responsible for answering such questions. Instead, their role is to offer a consistent and anticipated programming interface through their language. It is consistent to use an expression to represent a sequence of characters, which can then be represented by a variable. Thus, the task is accomplished.

From a subjective standpoint, it is possible that certain data could be sourced from an external location, with a dynamic schema. An option would be to represent this in a generic object format, which could result in the property names of the object being dynamic as well. The decision to use this approach ultimately depends on the developer’s discretion, and that of their colleagues during code review.

Inherited shoddy spaghetti code may require the use of dynamic naming as a necessary approach.

PHP’s responsibility is limited to providing a platform to write code, and it does not address the standard of the code’s design. Therefore, code review becomes essential to ensure the quality of the code.

variable variable is a type of reflection that poses the question, «If you are unaware of a variable prior to runtime, why would you consider changing it?

While not identical, a variable variable can be considered a distinct type of hash table (or array in php). Many variable variables can be rephrased as a hash table without causing surprise. However, if you require working with a variable both before and after runtime, dealing with a hash table may be even more challenging.

An instance of using settings that a user can modify serves as a straightforward use case. However, it should be noted that the following example is not secure in its current form, but it effectively illustrates its intended function.

query("SELECT `allowAccess`, `allowModify`, `allowDelete` FROM `user_settings` LIMIT 1")) < $row = $result->fetch_array(MYSQLI_ASSOC); $settings["allowAccess"] = $row["allowAccess"]; $settings["allowModify"] = $row["allowModify"]; $settings["allowDelete"] = $row["allowDelete"]; > /* Now consider you have a thousand settings and you dont want to write out every setting manually. */ if ($result = $mysqli->query("SELECT * FROM `user_settings` LIMIT 1")) < $row = $result->fetch_array(MYSQLI_ASSOC); foreach($row as $key => $val) < $settings[$key] = $val; >> /* Both options work, but everytime you want to use a setting you have to use something like below */ if ($settings["allowAccess"] && $settings["allowModify"] && $settings["allowDelete"]) < unlink($somefile); >/* Perhaps you would rather write */ if ($allowAccess && $allowModify && $allowDelete) < unlink($somefile); >/* Then you can use */ if ($result = $mysqli->query("SELECT * FROM `user_settings` LIMIT 1")) < $row = $result->fetch_array(MYSQLI_ASSOC); foreach($row as $key => $val) < //if you use extract, all columns are extracted, unless you drop them first. But perhaps you need those for something else. //now I extract the columns that start with allow and keep the columns like id, created, modified, etc. without the need to specify each column manually, which makes it easier if you ever decide to add another setting column. You don't need to update this part of the code. if (substr($key,0,5)=='allow') < $$key = $val; //$key = 'allowAccess', $$key == $allowAccess = $val; >> > ?> 

Here’s another instance to illustrate my point. I stumbled upon this example in the XHTML sanitizer for MediaWiki created by Brion Vibber . In his code, he has extensively employed arrays and encountered a situation where he had to reverse all of them. To do so, he utilized the following code:

While it is possible for him to have composed the given code, is it truly more legible?

Additionally, there is another scenario where I may want to choose which arrays to flip dynamically. By utilizing variable variable , I can effortlessly add new items to the array and flip them later on. In contrast, if I were to use the «typical» approach, I would have to create a loop with switch or if to manually add each option to the array.

PHP Variable Handling Functions, PHP Variable Handling Functions ; intval(), Returns the integer value of a variable ; is_array(), Checks whether a variable is an array ; is_bool(), Checks whether

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