Php if not exists function

How to Check if a Function Exists in PHP using function_exists()?

Learn how to check if a function exists in PHP using the built-in function_exists() method. Explore other PHP functions for checking function, method or class existence, and proper naming conventions for functions and classes in PHP.

• Using function_exists() in PHP
• Checking if a function exists in a class
• Other PHP functions for checking function, method or class existence
• Using isset() to check for function existence
• Proper naming conventions for functions and classes in PHP
• Other code samples for checking if a function exists in PHP
• Conclusion
• How to define function test () in PHP?
• What is an undefined function in PHP?
• How to check if a class has a function PHP?
• How do you know if a function exists?

If you are a PHP developer, you might have come across a situation where you need to check if a function exists before calling it. This can be especially important when working with large codebases or third-party libraries. Fortunately, PHP has a built-in function called function_exists() that allows developers to check if a function exists or not. In this article, we will guide you through the process of checking if a function exists in PHP and how to use the function_exists() method for this purpose.

Using function_exists() in PHP

The function_exists() function is a built-in PHP function that can check if a function exists or not. It takes a string parameter that specifies the name of the function to check. The function returns true if the function exists and is enabled, and false otherwise.

if (function_exists('function_name'))  // execute code > 

Developers can use function_exists() to check whether or not a PHP function is enabled for their website. This can be useful when working with third-party libraries or when writing code that needs to be compatible with different PHP versions.

Checking if a function exists in a class

To check if a function exists in a class, developers can use the method_exists() function in PHP. This function takes two parameters: the name of the class and the name of the method to check. The function returns true if the method exists and is enabled, and false otherwise.

if (method_exists('class_name', 'method_name'))  // execute code > 

The method_exists() function can check for methods within a class, which can be useful when working with object-oriented PHP code.

Other PHP functions for checking function, method or class existence

PHP has other functions like is_callable() , method_exists() , and class_exists() to check if a function, method, or class exists.

The is_callable() function checks if the contents of a variable can be called as a function or method. It takes a single parameter that can be a string or an array, and returns true if the contents of the parameter can be called as a function or method.

if (is_callable('function_name'))  // execute code > 

The class_exists() function checks if a specified class has been defined or not. It takes a single parameter that specifies the name of the class to check, and returns true if the class exists and is defined, and false otherwise.

if (class_exists('class_name'))  // execute code > 

Using isset() to check for function existence

The isset() function is used to check if a variable has been set and is not null. Developers can use isset() to check if a function exists by checking if the variable containing the function is set.

$function = 'function_name'; if (isset($function) && function_exists($function))  // execute code > 

This can be useful when working with dynamic function names or when passing function names as parameters to other functions.

Proper naming conventions for functions and classes in PHP

To avoid naming conflicts, developers should use proper naming conventions for functions and classes in PHP. Function names should be all lowercase with underscores separating words. Class names should be in CamelCase.

function my_function()  // code >class MyClass  // code > 

By following these naming conventions, developers can avoid conflicts with built-in php functions and classes , as well as third-party libraries.

Other code samples for checking if a function exists in PHP

In Php , for example, if function not exists php code sample

if(!function_exists('my_function')) < function myfunction()<>>

In Php , php check if function exists code example

function_exists('function_name'); //Will return true if function exists

In Php case in point, if function not exists php code sample

if(function_exists('my_function'))< // my_function is defined >

Conclusion

In conclusion, developers can use the function_exists() function in PHP to check if a function exists or not. Other PHP functions like method_exists() , is_callable() , and class_exists() can also be used for this purpose. Proper naming conventions for functions and classes should be followed to avoid naming conflicts. By using these techniques, developers can write more efficient and error-free code in PHP.

Источник

function_exists

Проверяет, есть ли в списке определённых функций, как встроенных, так и пользовательских, функция function_name .

Список параметров

Возвращаемые значения

Возвращает TRUE , если function_name существует и является функцией, иначе возвращается FALSE .

Замечание:

Эта функция возвращает FALSE для языковых конструкций, таких как include_once или echo .

Примеры

Пример #1 Пример использования function_exists()

if ( function_exists ( ‘imap_open’ )) echo «IMAP функции доступны.
\n» ;
> else echo «IMAP функции недоступны.
\n» ;
>
?>

Примечания

Замечание:

Обратите внимание, что название функции может присутствовать, даже если саму функцию невозможно использовать из-за настроек конфигурации или опций компиляции (например, как для функций image).

Смотрите также

• method_exists() — Проверяет, существует ли метод в данном классе
• is_callable() — Проверяет, может ли значение переменной быть вызвано в качестве функции
• get_defined_functions() — Возвращает массив всех определённых функций
• class_exists() — Проверяет, был ли объявлен класс
• extension_loaded() — Определение, загружено ли расширение

Источник

Using function_exists() to Check if Function Exists in php

In php, we can check if a function exists with the php function_exists() function.

if (function_exists('max')) < echo "max() exists!"; >else < echo "max() doesn't exist!"; >if (function_exists('other_function')) < echo "other_function() exists!"; >else < echo "other_function() doesn't exist!"; >//Output: max() exists! other_function() doesn't exist!

When working in php, it is useful to be able to check if a function exists or not.

To check if a function exists in our php program, we can use the function_exists() function. function_exists() takes a function name in the form of a string and checks to see if the function exists.

If the function exists, function_exists return true. Otherwise, function_exists returns false.

function_exists() can be useful so that we don’t try to call a function which hasn’t been defined and get an error.

Below are some examples of testing to see if a function exists in php.

if (function_exists('max')) < echo "max() exists!"; >else < echo "max() doesn't exist!"; >if (function_exists('other_function')) < echo "other_function() exists!"; >else < echo "other_function() doesn't exist!"; >//Output: max() exists! other_function() doesn't exist!

How to Check if a User Defined Function Exists in php with function_exists()

We can use the function_exists() function to check if a user defined function exists in our php code.

Below are some examples of checking for the existence of user defined functions in php with function_exists().

function exampleFunction($a) < return "What's up?"; >if (function_exists('exampleFunction')) < echo "exampleFunction() exists!"; >else < echo "exampleFunction() doesn't exist!"; function anotherFunction() < return "Not much."; >> if (function_exists('anotherFunction')) < echo "anotherFunction() exists!"; >else < echo "anotherFunction() doesn't exist!"; >// Output: exampleFunction() exists! anotherFunction() doesn't exist!

Hopefully this article has been useful for you to learn how to check if a function exists or not in php.

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