How to check if a variable is an integer with PHP
PHP has a variety of functions and approaches to determine if a variable is a
number and/or an integer. The problem is that many of the straight forward
approaches can result in false positives depending on how they react to type
juggling. Case in point, is_int() will return false for the string "123", we
could use is_numeric() but that will return true for both "123" and the
decimal number 1.23, and both functions will return true if you cast a string
as an integer like this: (int)"String!".
In the scenario where you want to determine if a variable is a string
(regardless if it's a string or a number to begin with) you can simply use
preg_match() to determine if the string contains just numbers:
preg_match('/^[0-9]+$/', trim($variable));
preg_match('/^\d+$/', trim($variable));Note that we trim the variable in the scenario when it's provided from user input, you can read more about it here](/how-to-strip-whitespace-from-a-string/).
There is another function that you could use but it is only meant to work on
strings and returns false if the variable is an actual integer. That function
is ctype_digit() and you can trick it by casting (string) when you call it:
ctype_digit(trim((string)$variable));If the $variable in question is known to always be a string (like in the case
of user input and often times data being returned from a database) you can
simply omit the cast, better safe than sorry though!