写一个 c++ boost 库获取 eth0 的网关的’代码

好的，以下是获取eth0网关的C++ Boost库代码：

#include <boost/asio.hpp>
#include <iostream>

using boost::asio::ip::tcp;

std::string get_gateway_address()
{
    boost::asio::io_service io_service;
    tcp::resolver resolver(io_service);
    tcp::resolver::query query(boost::asio::ip::host_name(), "");
    tcp::resolver::iterator iter = resolver.resolve(query);
    tcp::resolver::iterator end; // End marker.
    while (iter != end)
    {
        tcp::endpoint ep = *iter++;
        // Try to determine the default gateway for the network interface associated with this endpoint.
        struct
        {
            u_long Address;
            u_long Mask;
        } route;
        route.Address = ep.address().to_v4().to_ulong();
        route.Mask = 0xFFFFFFFF;
        DWORD dwRetVal;
        MIB_IPFORWARDROW ipForwardRow;
        dwRetVal = GetBestRoute(route.Address, 0, &ipForwardRow);
        if (dwRetVal == NO_ERROR)
        {
            tcp::endpoint gatewayEndpoint(boost::asio::ip::address_v4(ntohl(ipForwardRow.dwForwardNextHop)), 0);
            return gatewayEndpoint.address().to_string();
        }
    }
    return "";
}

int main()
{
    std::cout << "Default gateway address: " << get_gateway_address() << std::endl;
    return 0;
}

以上代码会获取当前主机的默认网关地址并把它作为std::string类型返回。您可以在您的项目中将以上代码编译为动态链接库或静态链接库来方便使用。