使用自定义操纵器我会这样做

Using a custom manipulator I'd do this

if (std::istringstream(date) >> std::noskipws
    >> day >> slash >> month >> slash >> year) {
    ...
}

操纵器看起来像这样:

std::istream& slash(std::istream& in) {
    if (in.peek() != '/') {
        in.setstate(std::ios_base::failbit);
    }
    return in;
}