C#的一些问题。 [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)] 的作用是什么？ 谢谢。

用系统自带的rasdial.exe可以实现
方法是 rasdial.exe 连接名称 用户名 密码
连接名称是你创建的宽带连接名 如"宽带连接"

System.Diagnostics.Process.Start("rasdial.exe", ADSLname.Text + " " + ADSLuser.Text + " " + ADSLpass.Text);

断线 rasdial.exe 连接名称 disconnect
System.Diagnostics.Process.Start("rasdial.exe", ADSLname.Text + " disconnect");

using System;
using System.Runtime.InteropServices;

public struct RASCONN
{
public int dwSize;
public IntPtr hrasconn;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=257)]
public string szEntryName;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=17)]
public string szDeviceType;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=129)]
public string szDeviceName;
}

[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Auto)]
public struct RasStats
{
public int dwSize;
public int dwBytesXmited;
public int dwBytesRcved;
public int dwFramesXmited;
public int dwFramesRcved;
public int dwCrcErr;
public int dwTimeoutErr;
public int dwAlignmentErr;
public int dwHardwareOverrunErr;
public int dwFramingErr;
public int dwBufferOverrunErr;
public int dwCompressionRatioIn;
public int dwCompressionRatioOut;
public int dwBps;
public int dwConnectionDuration;
}

[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Auto)]
public struct RasEntryName
{
public int dwSize;
//[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]
public string szEntryName;
//#if WINVER5
// public int dwFlags;
// [MarshalAs(UnmanagedType.ByValTStr,SizeConst=260+1)]
// public string szPhonebookPath;
//#endif
}
public class RAS

{

[DllImport("Rasapi32.dll", EntryPoint="RasEnumConnectionsA",
SetLastError=true)]

internal static extern int RasEnumConnections
(
ref RASCONN lprasconn, // buffer to receive connections data
ref int lpcb, // size in bytes of buffer
ref int lpcConnections // number of connections written to buffer
);

[DllImport("rasapi32.dll",CharSet=CharSet.Auto)]
internal static extern uint RasGetConnectionStatistics(
IntPtr hRasConn, // handle to the connection
[In,Out]RasStats lpStatistics // buffer to receive statistics
);
[DllImport("rasapi32.dll",CharSet=CharSet.Auto)]
public extern static uint RasHangUp(
IntPtr hrasconn // handle to the RAS connection to hang up
);

[DllImport("rasapi32.dll",CharSet=CharSet.Auto)]
public extern static uint RasEnumEntries (
string reserved, // reserved, must be NULL
string lpszPhonebook, // pointer to full path and
// file name of phone-book file
[In,Out]RasEntryName[] lprasentryname, // buffer to receive
// phone-book entries
ref int lpcb, // size in bytes of buffer
out int lpcEntries // number of entries written
// to buffer
);

[DllImport("wininet.dll",CharSet=CharSet.Auto)]
public extern static int InternetDial(
IntPtr hwnd,
[In]string lpszConnectoid,
uint dwFlags,
ref int lpdwConnection,
uint dwReserved
);

public RAS()
{

}

}
public enum DEL_CACHE_TYPE //要删除的类型。
{
File,//表示internet临时文件
Cookie //表示Cookie
};
public class RASDisplay
{
[DllImport("wininet.dll",CharSet=CharSet.Auto)]
public static extern bool DeleteUrlCacheEntry(
DEL_CACHE_TYPE type
);
private string m_duration;
private string m_ConnectionName;
private string[] m_ConnectionNames;
private double m_TX;
private double m_RX;
private bool m_connected;
private IntPtr m_ConnectedRasHandle;

//RasStats status = new RasStats();
public RASDisplay()
{
m_connected = true;

RAS lpras = new RAS();
RASCONN lprasConn = new RASCONN();

lprasConn.dwSize = Marshal.SizeOf(typeof(RASCONN));
lprasConn.hrasconn = IntPtr.Zero;

int lpcb = 0;
int lpcConnections = 0;
int nRet = 0;
lpcb = Marshal.SizeOf(typeof(RASCONN));

nRet = RAS.RasEnumConnections(ref lprasConn, ref lpcb, ref
lpcConnections);

if(nRet != 0)

{
m_connected = false;
return;

}

if(lpcConnections > 0)
{

//for (int i = 0; i < lpcConnections; i++)

//{
RasStats stats = new RasStats();

m_ConnectedRasHandle = lprasConn.hrasconn;
RAS.RasGetConnectionStatistics(lprasConn.hrasconn, stats);

m_ConnectionName = lprasConn.szEntryName;

int Hours = 0;
int Minutes = 0;
int Seconds = 0;

Hours = ((stats.dwConnectionDuration /1000) /3600);
Minutes = ((stats.dwConnectionDuration /1000) /60) - (Hours * 60);
Seconds = ((stats.dwConnectionDuration /1000)) - (Minutes * 60) - (Hours * 3600);

m_duration = Hours + " hours " + Minutes + " minutes " + Seconds + " secs";
m_TX = stats.dwBytesXmited;
m_RX = stats.dwBytesRcved;

//}

}
else
{
m_connected = false;
}

int lpNames = 1;
int entryNameSize = 0;
int lpSize = 0;
RasEntryName[] names = null;

entryNameSize=Marshal.SizeOf(typeof(RasEntryName));
lpSize=lpNames*entryNameSize;

names=new RasEntryName[lpNames];
names[0].dwSize=entryNameSize;

uint retval = RAS.RasEnumEntries(null,null,names,ref lpSize,out lpNames);

//if we have more than one connection, we need to do it again
if(lpNames > 1)
{
names=new RasEntryName[lpNames];
for(int i=0;i<names.Length;i++)
{
names[i].dwSize=entryNameSize;
}

retval = RAS.RasEnumEntries(null,null,names,ref lpSize,out lpNames);

}
m_ConnectionNames = new string[names.Length];

if(lpNames>0)
{
for(int i=0;i<names.Length;i++)
{

m_ConnectionNames[i] = names[i].szEntryName;

}
}
}

public string Duration
{
get
{
return m_connected ? m_duration : "";
}
}

public string[] Connections
{
get
{
return m_ConnectionNames;
}
}

public double BytesTransmitted
{
get
{
return m_connected ? m_TX : 0;
}
}
public double BytesReceived
{
get
{
return m_connected ? m_RX : 0;

}
}
public string ConnectionName
{
get
{
return m_connected ? m_ConnectionName : "";
}
}
public bool IsConnected
{
get
{
return m_connected;
}
}

public int Connect(string Connection)
{
int temp = 0;
uint INTERNET_AUTO_DIAL_UNATTENDED = 2;
int retVal = RAS.InternetDial(IntPtr.Zero,Connection,INTERNET_AUTO_DIAL_UNATTENDED,ref temp,0);
return retVal;
}
public void Disconnect()
{
RAS.RasHangUp(m_ConnectedRasHandle);
}
}

用法是
RASDisplay ras = new RASDisplay();
ras.Disconnect();//断线
ras.Connect("adsl");//拨号