The scope of a variable is defined as its range in the program under which it can be accessed. In other words, “The scope of a variable is the portion of the program within which it is defined and can be accessed.”
PHP has three types of variable scopes:
- Local variable
- Global variable
- Static variable
Local variable
The variables declared within a function are called local variables to that function and has its scope only in that particular function. In simple words, it cannot be accessed outside that function. Any declaration of a variable outside the function with same name as that of the one within the function is a complete different variable. We will learn about functions in detail in later articles. For now, consider a function as a block of statements.
Ex.1
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<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>local variable</title> </head> <body> <?php function local_var() { $num = 50; //local variable echo "Local variable declared inside the function is: ". $num; } local_var(); ?> </body> </html> |
Output:
Local variable declared inside the function is: 50
Ex.2
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<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>local variable</title> </head> <body> <?php function mytest() { $lang = "PHP"; echo "Web development language: " .$lang; } mytest(); //using $lang (local variable) outside the function will generate an error echo $lang; ?> </body> </html> |
Output:
Web development language: PHP
Notice: Undefined variable: lang in C:\xampp\htdocs\dkyadav\index.php on line 16
Global variable
The variables declared outside a function are called global variables. These variables can be accessed directly outside a function. To get access within a function we need to use the “global” keyword before the variable to refer to the global variable.
Ex.1
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<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>global variable</title> </head> <body> <?php $name = "Dharmendra Yadav"; //Global Variable function myweb() { global $name; echo "Variable inside the function: ". $name; echo "</br>"; } myweb(); echo "Variable outside the function: ". $name; ?> </body> </html> |
Output:
Variable inside the function: Dharmendra Yadav
Variable outside the function: Dharmendra Yadav
Note: Without using the global keyword, if you try to access a global variable inside the function, it will generate an error that the variable is undefined.
Ex.2
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<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>global variable</title> </head> <body> <?php $name = "Dharmendra Yadav"; //Global Variable function myweb() { echo "Variable inside the function: ". $name; echo "</br>"; } myweb(); ?> </body> </html> |
Output:
Notice: Undefined variable: name in C:\xampp\htdocs\dkyadav\index.php on line 12
Variable inside the function:
Ex.3
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<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>global variable</title> </head> <body> <?php $x = 5; //global variable $y = 13; //global variable function myweb() { $sum = $GLOBALS['x'] + $GLOBALS['y']; echo "Sum of global variables is: " .$sum; } myweb(); ?> </body> </html> |
Output:
Sum of global variables is: 18
If two variables, local and global, have the same name, then the local variable has higher priority than the global variable inside the function.
Ex.4
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<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>global variable</title> </head> <body> <?php $x = 5; function myweb() { $x = 7; echo "value of x: ".$x; } myweb(); ?> </body> </html> |
Output:
value of x: 7
Note: local variable has higher priority than the global variable.
Static variable
It is the characteristic of PHP to delete the variable, ones it completes its execution and the memory is freed. But sometimes we need to store the variables even after the completion of function execution. To do this we use static keyword and the variables are then called as static variables. PHP associates a data type depending on the value for the variable.
Ex.1
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<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>static variable</title> </head> <body> <?php function myweb() { static $x = 3; //static variable $y = 6; //Non-static variable //increment in non-static variable $x++; //increment in static variable $y++; echo "Static: " .$x ."</br>"; echo "Non-static: " .$y ."</br>"; } //first function call myweb(); //second function call myweb(); ?> </body> </html> |
Output:
Static: 4
Non-static: 7
Static: 5
Non-static: 7
You have to notice that $x regularly increments after each function call, where as $y does not. This is why because $y is not a static variable, so it freed its memory after the execution of each function call.
