IPv4 的封装

ipv4.cpp

#define let auto const

class Ipv4 {
  public:
    using Value = std::array<uint8_t, 4>;
    static constexpr auto ipv4_str_max_size = 3 + 1 + 3 + 1 + 3 + 1 + 3 + 1;

  public:
    explicit Ipv4(char const * ipv4, bool strict = false):
        Ipv4(ipv4, -1, strict) {}
    explicit Ipv4(std::string const & ipv4, bool strict = false):
        Ipv4(ipv4.c_str(), ipv4.size(), strict) {}

  public:
    // IPv4 的大端表示
    explicit operator uint32_t() const noexcept {
        return reinterpret_cast<uint32_t const &>(*ipv4_.data());
    }
    explicit operator std::string() const;
    auto to_string(std::string & ipv4) const noexcept -> void;
    auto to_string(char * ipv4, size_t buf_size) const noexcept
            -> size_t;
    auto raw() const noexcept -> Value { return ipv4_; }

  private:
    explicit Ipv4(char const * ipv4, size_t size, bool strict);
    auto to_string_safe(char (&ipv4)[Ipv4::ipv4_str_max_size]) const noexcept
            -> size_t;

  private:
    Value ipv4_ = {};   // 大端

  private:
    friend auto operator<<(std::ostream & out, Ipv4 & ipv4) -> std::ostream &;
    friend auto operator>>(std::istream & out, Ipv4 & ipv4) -> std::istream &;
};  // class Ipv4

Ipv4::Ipv4(char const * ipv4, size_t size, bool strict) {
    auto ip = std::array<int, 4>();
    auto valid =
        std::sscanf(ipv4, "%d.%d.%d.%d", &ip[0], &ip[1], &ip[2], &ip[3]) == 4;
    for (auto n: ip) {
        valid = valid && (0 <= n && n <= 255);
    }
    if (valid && strict) {
        char buf[Ipv4::ipv4_str_max_size];

        valid = true
            && (this->to_string_safe(buf) == size || size == -1)
            && std::strcmp(ipv4, buf)
        ;
    }
    if (!valid) { throw std::invalid_argument(ipv4); }
    for (auto i = 0; i != ipv4_.size(); ++i) {
        ipv4_[i] = ip[i];
    }
}

Ipv4::operator std::string() const {
    auto ipv4 = std::string();
    this->to_string(ipv4);
    return ipv4;
}

auto Ipv4::to_string(std::string & ipv4) const noexcept -> void {
    char buf[Ipv4::ipv4_str_max_size];
    let size = this->to_string_safe(buf);
    ipv4.clear();
    ipv4.append(buf, size);
}

auto Ipv4::to_string(char * ipv4, size_t buf_size) const noexcept -> size_t {
    char buf[Ipv4::ipv4_str_max_size];
    let size = this->to_string_safe(buf);
    if (buf_size <= size) { return 0; }
    std::copy_n(buf, size + 1, ipv4);   // 末尾 '\0'
    return size;
}

auto Ipv4::to_string_safe(char (&ipv4)[Ipv4::ipv4_str_max_size]) const noexcept
        -> size_t {
    let size = std::sprintf(ipv4, "%d.%d.%d.%d",
        ipv4_[0], ipv4_[1], ipv4_[2], ipv4_[3]);
    assert(size < std::size(ipv4));
    return size;
}

auto operator<<(std::ostream & out, Ipv4 & ipv4) -> std::ostream & {
    char buf[Ipv4::ipv4_str_max_size];
    ipv4.to_string_safe(buf);
    out << buf;
    return out;
}

auto operator>>(std::istream & in, Ipv4 & ipv4) -> std::istream & {
    auto buf = std::string();
    in >> buf;
    ipv4.~Ipv4();
    new (&ipv4)Ipv4(buf);
    return in;
}