The mb_stristr() is an inbuilt function in PHP that is used to get the first occurrence of a string within another string. It will check case insensitivity.

Syntax:

mb_stristr(
    $haystack, 
    $needle, 
    $before_needle, 
    $encoding = null
): string|false

Parameters:

This function accepts 4 parameters that are described below:

• $haystack: This is the string parameter where we search for our first occurrence of the string.
• $needle: This is the substring that we want to search in the $haystack parameter.
• $before_needle: This is the optional parameter that determines whether to return haystack after or before $needle occurs. If this parameter is “true” it will return beginning to the first occurrence of the $needle string (excluding needle). If this parameter is set to “false”, It will return from the beginning of the $needle to the $needle end.
• $encoding: This is the optional parameter that specifies the character encoding in the $haystack and $needle parameters. If the encoding is not provided, it will use character encoding used.

Return Value:

This function returns the portion of $haystack if the needle is found in a $haystack, otherwise, it will return “false”.

Program 1: The following program demonstrates the mb_stristr() Function.

World

Program 2: The following program demonstrates the mb_stristr() Function.

bool(false)

Program 3: The following program demonstrates the mb_stristr() Function.

Substring 'WORLD' found in 'Hello World'

Reference: https://www.php.net/manual/en/function.mb-stristr.php