Character type checking

ctype_alnum - Check for alphanumeric character(s)
ctype_alpha - Check for alphabetic character(s)
ctype_cntrl - Check for control character(s)
ctype_digit - Check for numeric character(s)
ctype_graph - Check for any printable character(s) except space
ctype_lower - Check for lowercase character(s)
ctype_print - Check for printable character(s)
ctype_punct - Check for any printable character which is not whitespace or an alphanumeric character
ctype_space - Check for whitespace character(s)
ctype_upper - Check for uppercase character(s)
ctype_xdigit - Check for character(s) representing a hexadecimal digit