C#中判断本地系统的网络连接状态的方法

函数internetgetconnectedstate返回本地系统的网络连接状态。

语法：

bool internetgetconnectedstate(

__out lpdword lpdwflags,

__in dword dwreserved

);

 

参数：

lpdwflags[out]

指向一个变量，该变量接收连接描述内容。该参数在函数返回flase时仍可以返回一个有效的标记。该参数可以为下列值的一个或多个。

值	含义
internet_connection_configured0x40	local system has a valid connection to the internet, but it might or might not be currently connected.
internet_connection_lan 0x02	local system uses a local area network to connect to the internet.
internet_connection_modem0x01	local system uses a modem to connect to the internet.
internet_connection_modem_busy0x08	no longer used.
internet_connection_offline 0x20	local system is in offline mode.
internet_connection_proxy0x04	local system uses a proxy server to connect to the internet.
internet_ras_installed0x10	local system has ras installed.

dwreserved[in]

保留值。必须为0。

 

返回值：

当存在一个modem或一个lan连接时，返回true，当不存在internet连接或所有的连接当前未被激活时，返回false。

当该函数返回false时，程序可以调用getlasterror来接收错误代码。

 

示例：

using system;
using system.collections.generic;
using system.linq;
using system.text;
using system.threading.tasks;
using system.runtime.interopservices;

namespace consoleapplication1
{
    class program
    {
        private const int internet_connection_modem = 1;

        private const int internet_connection_lan = 2;

        private const int internet_connection_proxy = 4;

        private const int internet_connection_modem_busy = 8;

        [dllimport("wininet.dll ")]

        //声明外部的函数：

        private static extern bool internetgetconnectedstate(
            ref  int flag,
            int dwreserved
        );

        static void main(string[] args)
        {
            int flag = 0;

            string netstates = "";

            if (!internetgetconnectedstate(ref flag, 0))
            {
                console.writeline("no！");
            }
            else
            {

                if ((flag & internet_connection_modem) != 0)

                    netstates += " connect by modem /n";

                if ((flag & internet_connection_lan) != 0)

                    netstates += "connect by lan  /n";

                if ((flag & internet_connection_proxy) != 0)

                    netstates += "connect by proxy /n";

                if ((flag & internet_connection_modem_busy) != 0)

                    netstates += " modem is busy  /n";

            }

            console.writeline(netstates);
            console.readline();
        }
    }
}

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