If the "This" is found in $string, strpos() will return 0, but it will be of type integer. Luckily, PHP comes to the rescue with the = operator, which, if you recall, means "is identical to", which means $pos must be equal to false and of the same type as false (boolean). However, PHP considers 0 to be the same value as false, which means that our if statement cannot tell the difference between "Substring not found" and "Substring found at index 0" - quite a problem! This time the problem lies in the fact that "This" is the first thing in $string, which means that strpos() will return 0. Is it another case sensitivity problem? Not quite. If you try executing that, you will find that it outputs "Not found", despite "This" quite clearly being in $string. If the substring sent in parameter two is not found in parameter one, strpos() will return false.
You can specify whole words in parameter two, which will make strpos() return the first position of that word within the string, for example strpos($string, "test") would return 19 - the index of the first letter in the matched word. Remember that PHP considers the first letter of a string to be index 0, which means that the A strpos() found is actually the ninth character. That will return 8, because the first character in "This is a strpos() test" that is a lowercase A is at index 8. It is easier to explain in code, so here goes: Strpos(), and its case-insensitive sibling stripos(), returns the index of the first occurrence of a substring within a string. Int stripos ( string haystack, string needle ) Knowing whether a string of text contains another string – a word or other text value – is imperative for parsing and understanding user input, or extracting useful information from database queries.Int strpos ( string haystack, string needle )
Notice we use the = operator to check both value and type so that a return of 0 does not incorrectly indicate that the string was not found. To demonstrate, we use an if statement to check the presence of “blue” in $vehicle_description, and then print some text to the browser with information based on the outcome. $car_is_blue = strpos($vehicle_description, "blue") $vehicle_description = "big red shiny car" If checking the result from str_pos() using an if statement, you must check explicitly whether the result is equal to FALSE to ensure the correct action is taken. This can’t be done when checking the results that return an index! As indexes start counting at 0 (zero), zero represents a positive result. 
In programming, 0 and FALSE are often treated as indicating a false value. $car_is_big returns 0 as the word “big” appears at the very beginning of $vehicle_description – which is index 0. $car_is_blue returns FALSE as the word “blue” does NOT appear anywhere in $vehicle_description. $car_is_red returns 4 as the word “red” appears starting at the 4th index (position) in $vehicle_description. $car_is_big_ignore_first_word = strpos($vehicle_description, "big", 3) // FALSE $car_is_big = strpos($vehicle_description, "big") // 0 $car_is_blue = strpos($vehicle_description, "blue") // FALSE $car_is_red = strpos($vehicle_description, "red") // 4 You must check that the value returned is explicitly not equal to FALSE using = to make sure the correct action is takenĪs an example we can check whether a string describing a car contains keywords: $vehicle_description = "big red shiny car". This is very important if using boolean logic and if statements to check whether the string was found. If $needle is not found in $haystack strpos() will return FALSE. 
The position will start at 0 – needle is at position 0 if $haystack immediately starts with $needle. Returns an integer representing the position of $needle within $haystack. If it is negative the search will start after that number of characters from the end of $haystack. If it is positive the search will start after that number of characters from the beginning of $haystack. $offset Is optional and defines where the search should start. $needle is the string search term we are looking for. STR POS SERIES
$haystack is the string (text or series of characters) we want to search within. It is a great companion to the PHP substr()and str_replace() functions for processing text data. The PHP strpos() function checks whether a string is contained within another string – for example checking whether a certain word appears in a sentence, and what position it appears in.
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