无法根据需要评估表达式匹配

Question

I need to implement a code in PHP which adds a new city (passed in $_POST['City']) name in database for a given $stateID if it does not already exist and returns its CityID generated, else use the CityID passed in $_POST['City']. Here is the code:

$stateID = substr(filter_input(INPUT_POST, 'State'), 0, 2);
$city = filter_input(INPUT_POST, 'City', FILTER_VALIDATE_INT);
$cityID = NULL;
if(!preg_match("/[a-zA-Z]/", $city)){
  $cityID = $city;
  echo 'City Exists';
}
else{
  # If a new city name is entered, store it in database
  $params = array('ss', $stateID, $city);
  $cityID = $dbh->ExecuteScalar("CALL AddNewCity(?, ?, @outCityID)", $params);
  echo 'New City Added';
}

Problem is, whether the value of $city is like ABC or like 123, the code echoes City Exists.

Please ignore the code $dbh->ExecuteScalar......... It is using my custom built database handling library.

What is wrong with the regular expression statement?

Answer 1

The regex [a-zA-Z] matches a lower or uppercase character and preg_match returns 1 if the pattern matches given subject, 0 if it does not, or FALSE if an error occurred.

You use filter_input with FILTER_VALIDATE_INT.

If you enter ABC, the value of $city will be false and preg_match("/[a-zA-Z]/", false) will return 0. The if statement will check for if (!0) which will be true and you will see City Exists

If you enter 123 the value of $city will be 123 and preg_match("/[a-zA-Z]/", 123) will return 0. The if statement will check for if (!0) which will be true and you will see City Exists