isAlphaNumeric function
Implementation
bool isAlphaNumeric(int c) {
if (c < _codeUnit_0 ||
c > _codeUnit_z ||
((c > _codeUnit_9 && c < _codeUnit_A) ||
(c > _codeUnit_Z && c < _codeUnit_a && c != _codeUnit__))) {
return false;
}
return true;
}