is string numeric

i didnt find this function in the manual.. in coldfusion there is a isnumeric function which returns true or false if a string only contains numbers.. i think this would be a nice function to include in php? :) there is currently a gettype function .. with this i get $a = "12345"; echo gettype($a); // displays "string" $b = 12345; echo gettype($b); // displays "integer" is_numeric could work this way $a = "12345"; // or $a = 12345; echo is_numeric($a); // true $b = "12345a"; echo is_numeric($b); // false intval is not what im after here.. if there is already a function that does this, can you point me to the location of it in the manual.. thanks Harald