PHP unset() Function

The unset() function is used to reset any variable that has been defined earlier. Two types of variables are used in any programming language. One is a global variable and another is a local variable. The variable defined outside the function is called a global variable that is accessible from anywhere in the script. The variable defined inside the function is called a local variable that is accessible inside the function only.

If the unset function is used for the local and global variables, then it resets both variables locally. That means the value of the global variable remains unchanged that was defined before changing inside the function. The $GLOBALS array or global keyword can be used to unset the global variable permanently. The uses of this function to reset PHP variables have shown in this tutorial.

Syntax

This function can take multiple variables of different data types to delete and it returns nothing. The syntax of this function has given below.

The first argument of this function is mandatory. The other optional arguments can be used in this function to delete multiple variables.

Uses of unset() Function

The use of the unset() function to delete one or more variables has shown in this part of the tutorial.

Example-1: Reset the Global Variable

Create a PHP file with the following script to check the way of deleting a variable using the unset() variable. In the script, a float variable has been declared that has been deleted later using the unset() function. The variable has printed before delete and after deleting it.

Output:

The following output will appear after executing the above script. The warning messages have printed in the output after deleting the variable.

Example-2: Reset the Global Variable Inside the Function

Create a PHP file with the following script to check how the global variable works when the variable is deleted inside the function. The global variable named $num has been declared in the script and 10 has been added with the variable and deleted the variable using the unset() function inside the function named unsetGlobal(). The $num has printed before and after calling the unsetGlobal() function.

Output:

The following output will appear after executing the above script. According to the output, the global variable has not been destroyed inside the function.

Example-3: Reset the Global Variable with GLOBALS Array

The GLOBALS array is required to unset the global variables inside the function. Create a PHP file with the following script to unset a global variable inside a function by defining the global with GLOBALS array in the unset() function. The isset() function has been used in the script to remove the warming message after deleting the variable.

Output:

The following output will appear after executing the above script.

Example-4: Reset the Variable Pass by Reference

Create a PHP file with the following script to check the way of removing the variable that is passed by reference in the function. A string variable has been defined and passed by reference in the function named combineString(). The variable has been deleted after concatenating a string value inside the function. The variable has printed before and after calling the function and inside the function after delete.

Output:

The following output will appear after executing the above script. The output shows that the variable has been deleted locally and the global variable contains the modified value.

Example-5: Reset Static Variable

Create a PHP file with the following script to check how the static variable works after removing it inside the function. The unsetStaticVariable() function has been called three times to check the output of the static variables.

Output:

The following output will appear after executing the above script.

Conclusion

Different examples of unset() function have been shown in this tutorial to unset the global, reference, and static variables that will help the PHP users to know the purpose of this function properly.