PHP Variables
PHP Data Types
PHP Echo & Print
PHP Strings
PHP Numbers
PHP Constants
PHP Operators
PHP if...else...elseif Statements
Switch Statement
PHP Loops
PHP Arrays
Superglobals
PHP Coding Standards
PHP Form Handling
PHP Form Validation
PHP URLs Validation
PHP Form Required Validation
Complete Form Example
PHP File Functions Open/Read
PHP File Create/Write
PHP File Upload
PHP Cookies Handling
PHP Session Handling
PHP filter_var() Function
PHP Validation Filters
PHP Sanitization Filters
Using Filters
Filters Advanced
JSON
PHP Date and Time
MySQL Database
MySQL Connect
MySQL Commands-Creating a Table
MySQL Commands-Inserting The data
MySQL Commands-Prepared Statement
MySQL Commands-Selecting The Data
MySQL Commands-Where and Order By
MySQL Commands-Deleting And Updating The Data
PHP-OOP Introduction
PHP-Classes/Objects
PHP-Constructor/Destructor
PHP-Access Modifiers
PHP-Inheritance
PHP-Inheritance and Protected Access Modifier
PHP-Overriding Inherited Methods
PHP-Final keyword
PHP-Abstract Classes
PHP-Constants
PHP-Traits
PHP-Static Methods and Properties
Introduction to Functions
Defining A function
Returning Values From A Function
Dynamic Function Calls
Variable Scope
Understanding Arguments Or Parameters
Testing For A Function Existence
Returning Multiple Values From A Function
Making practical Use By Building Code Libraries For Code Re-usability
Using Include() And Require()
A function present in php checks the existence of another function. function_exists is the function that checks whether a function is available in php or not. It gives true value if the function is present in php.
function_exists check the file functions.php if the function is present in some other php file and we are trying to call in our current file. If we do not check function_exists and our function is present in any other file it will throw an error at runtime mentioning Call to undefined function.
It prevents php fatal error for a webpage and allows you to choose the other set of code that should run when the file is deleted or not present in functions.php.
You can use function_exists as below.
if (function_exists(‘greeting’))
{
greeting();
}
else
{
echo “Sorry, the function is missing”;
}
?>
So, if in any other file, greeting function exists, the function is called otherwise the else statement will run and mention the function is missing instead of a fatal error in php.
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