constexpr network_v4 make_network_v4(const address_v4& addr, int prefix_len);
Returns: network_v4(addr, prefix_len).
constexpr network_v4 make_network_v4(const address_v4& addr, const address_v4& mask);
Returns: network_v4(addr, mask).
network_v4 make_network_v4(const char* str);
network_v4 make_network_v4(const char* str, error_code& ec) noexcept;
network_v4 make_network_v4(const string& str);
network_v4 make_network_v4(const string& str, error_code& ec) noexcept;
network_v4 make_network_v4(string_view str);
network_v4 make_network_v4(string_view str, error_code& ec) noexcept;
Returns: If str contains a value of the form address '/' prefix-length, a network_v4 object constructed with the result of applying make_address_v4() to the address portion of the string, and the result of converting prefix-length to an integer of type int. Otherwise returns network_v4() and sets ec to reflect the error.