如何枚举本地的连接

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一年前，用VC++做了一个取得和设置本地计算机的网络信息的程序。其中的网络信息包括，网卡，调制解调器，网络打印机等。一年后，另外的一个项目用到了调制解调器这一部分。打开以前的工程，看到当初那么熟悉的代码，感觉有点陌生了。

借这次重温的机会，把其中的一些东西写下来，即作为技术记录或总结，也可以供大家参考。虽然这次是重温，不过需要用C#来实现。如果时间上允许的话将把C#的那一部分也放上来。希望对他人能有些帮助。

首先，需要枚举出所有连接的名字。Windows中提供了RasEnumEntries函数。在MSDN中对这个函数的说明是“The RasEnumEntries function lists all entry names in a remote access phone book.”。其中“phone book”还不能用汉语正确的表述，不过我想应该是类是一个电话簿，其中记录了所有的网络连接。RasEnumEntries原型如下：

DWORD RasEnumEntries(

  LPCTSTR reserved,

  LPTCSTR lpszPhonebook,

  LPRASENTRYNAME lprasentryname,

  LPDWORD lpcb,

  LPDWORD lpcEntries

);

reserved，是保留参数，必须设置为NULL。

lpszPhonebook，制定一个“phone-book”文件的名称，如果设置成NULL,那么系统使用的是默认的“phone-book”文件的名称。

lprasentryname，RASENTRYNAME结构体的缓冲区。这个函数会把每一个“phone-book”填充到这个缓冲区数组中。

lpcb，传入RASENTRYNAME结构体的大小，返回成功写入的字节大小。

lpcEntries，返回找到连接的数量。

RasEnumEntries结构体格式如下：

typedef struct _RASENTRYNAME {

  DWORD  dwSize;

  TCHAR  szEntryName[RAS_MaxEntryName + 1];

#if (WINVER >= 0x500)

  DWORD dwFlags;

  TCHAR  szPhonebookPath[MAX_PATH + 1];

#endif

} RASENTRYNAME;

MSDN中的说明是“The RASENTRYNAME structure contains an entry name from a remote access phone book.”可以看出，这个结构体存储着连接的名称。这就是我们想得到的。在使用这个结构体的时候，先要设置dwSize成员的值。

如果你在MSDN中查找RasEnumEntries在Remarks里可以看到微软提供的一个实例，很好用的噢，呵呵。为了方便阅读把这个里贴在下面：

DWORD dwCb = sizeof(RASENTRYNAME);

    DWORD dwErr = ERROR_SUCCESS;

    DWORD dwRetries = 5;

    DWORD dwEntries = 0;

    RASENTRYNAME* lpRasEntryName = NULL;

//

    // Loop through in case the information from RAS changes between calls.

    while (dwRetries--)

        // If the memory is allocated, free it.

//

        if (NULL != lpRasEntryName)

            HeapFree(GetProcessHeap(), 0, lpRasEntryName);

            lpRasEntryName = NULL;

        // Allocate the size need for the RAS structure.

//

        lpRasEntryName = HeapAlloc(GetProcessHeap(), 0, dwCb);

        if (NULL == lpRasEntryName)

            dwErr = ERROR_NOT_ENOUGH_MEMORY;

            break;

//

        // Set the structure size for version checking purposes.

        lpRasEntryName->dwSize = sizeof(RASENTRYNAME);

//

        // Call the RAS API, bail on the loop if we are successful or an unknown

        // error occurs.

        dwErr = RasEnumEntries(

                    NULL,

                    NULL,

                    lpRasEntryName,

                    &dwCb,

                    &dwEntries);

        if (ERROR_BUFFER_TOO_SMALL != dwErr)

            break;

//

    // In the success case print the names of the entries.

    if (ERROR_SUCCESS == dwErr)

        DWORD i;

        printf("Phone-book entries in the default phone book:/n/n");

        for (i = 0; i < dwEntries; i++)

            printf("%s/n", lpRasEntryName[i]->szEntryName);

    else

        printf("RasEnumEntries failed: Error = %d/n", dwErr);

//

    // Free the memory if necessary.

    if (NULL != lpRasEntryName)

        HeapFree(GetProcessHeap(), 0, lpRasEntryName);

        lpRasEntryName = NULL;

}

  在C#下使用API函数不能像VC++那样直接使用，需要进行

  重新声明。而所用到的结构体也要重新定义。VC++中有好

  多数据类型在C#下有不能得到支持，因此在重新定义结构体

  的时候还需要进行数据类型的替换。

  上面提到了RasEnumEntries和RASENTRYNAME。

  它们在C#下的声明和定义如下：

ternal enum RasFieldSizeConstants

{

RAS_MaxDeviceType = 16,

RAS_MaxPhoneNumber = 128,

RAS_MaxIpAddress = 15,

RAS_MaxIpxAddress = 21,

#if WINVER4

RAS_MaxEntryName = 256,

RAS_MaxDeviceName = 128,

RAS_MaxCallbackNumber = RAS_MaxPhoneNumber,

#else

RAS_MaxEntryName = 20,

RAS_MaxDeviceName = 32,

RAS_MaxCallbackNumber = 48,

#endif

RAS_MaxAreaCode = 10,

RAS_MaxPadType = 32,

RAS_MaxX25Address = 200,

RAS_MaxFacilities = 200,

RAS_MaxUserData = 200,

RAS_MaxReplyMessage = 1024,

RAS_MaxDnsSuffix = 256,

UNLEN = 256,

PWLEN = 256,

DNLEN = 15

}

[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Auto)]

public struct RasEntryName

{

public int dwSize;

[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]

public string szEntryName;

[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]

public string szEntryName;

[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

}

 [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
           )
     具体的信息还请参考MSDN，这里更全面，更具有权威性。

ternal enum RasFieldSizeConstants

{

RAS_MaxDeviceType = 16,

RAS_MaxPhoneNumber = 128,

RAS_MaxIpAddress = 15,

RAS_MaxIpxAddress = 21,

#if WINVER4

RAS_MaxEntryName = 256,

RAS_MaxDeviceName = 128,

RAS_MaxCallbackNumber = RAS_MaxPhoneNumber,

#else

RAS_MaxEntryName = 20,

RAS_MaxDeviceName = 32,

RAS_MaxCallbackNumber = 48,

#endif

RAS_MaxAreaCode = 10,

RAS_MaxPadType = 32,

RAS_MaxX25Address = 200,

RAS_MaxFacilities = 200,

RAS_MaxUserData = 200,

RAS_MaxReplyMessage = 1024,

RAS_MaxDnsSuffix = 256,

UNLEN = 256,

PWLEN = 256,

DNLEN = 15

}

[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Auto)]

public struct RasEntryName

{

public int dwSize;

[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]

public string szEntryName;

[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]

public string szEntryName;

[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

}

 [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
           )
     具体的信息还请参考MSDN，这里更全面，更具有权威性。

ternal enum RasFieldSizeConstants

{

RAS_MaxDeviceType = 16,

RAS_MaxPhoneNumber = 128,

RAS_MaxIpAddress = 15,

RAS_MaxIpxAddress = 21,

#if WINVER4

RAS_MaxEntryName = 256,

RAS_MaxDeviceName = 128,

RAS_MaxCallbackNumber = RAS_MaxPhoneNumber,

#else

RAS_MaxEntryName = 20,

RAS_MaxDeviceName = 32,

RAS_MaxCallbackNumber = 48,

#endif

RAS_MaxAreaCode = 10,

RAS_MaxPadType = 32,

RAS_MaxX25Address = 200,

RAS_MaxFacilities = 200,

RAS_MaxUserData = 200,

RAS_MaxReplyMessage = 1024,

RAS_MaxDnsSuffix = 256,

UNLEN = 256,

PWLEN = 256,

DNLEN = 15

}

[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Auto)]

public struct RasEntryName

{

public int dwSize;

[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]

public string szEntryName;

[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]

public string szEntryName;

[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

}

 [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
           )
     具体的信息还请参考MSDN，这里更全面，更具有权威性。

  在C#下使用API函数不能像VC++那样直接使用，需要进行

  重新声明。而所用到的结构体也要重新定义。VC++中有好

  多数据类型在C#下有不能得到支持，因此在重新定义结构体

  的时候还需要进行数据类型的替换。

  上面提到了RasEnumEntries和RASENTRYNAME。

  它们在C#下的声明和定义如下：

ternal enum RasFieldSizeConstants

{

RAS_MaxDeviceType = 16,

RAS_MaxPhoneNumber = 128,

RAS_MaxIpAddress = 15,

RAS_MaxIpxAddress = 21,

#if WINVER4

RAS_MaxEntryName = 256,

RAS_MaxDeviceName = 128,

RAS_MaxCallbackNumber = RAS_MaxPhoneNumber,

#else

RAS_MaxEntryName = 20,

RAS_MaxDeviceName = 32,

RAS_MaxCallbackNumber = 48,

#endif

RAS_MaxAreaCode = 10,

RAS_MaxPadType = 32,

RAS_MaxX25Address = 200,

RAS_MaxFacilities = 200,

RAS_MaxUserData = 200,

RAS_MaxReplyMessage = 1024,

RAS_MaxDnsSuffix = 256,

UNLEN = 256,

PWLEN = 256,

DNLEN = 15

}

[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Auto)]

public struct RasEntryName

{

public int dwSize;

[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]

public string szEntryName;

[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]

public string szEntryName;

[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

}

 [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
           )
     具体的信息还请参考MSDN，这里更全面，更具有权威性。

ternal enum RasFieldSizeConstants

{

RAS_MaxDeviceType = 16,

RAS_MaxPhoneNumber = 128,

RAS_MaxIpAddress = 15,

RAS_MaxIpxAddress = 21,

#if WINVER4

RAS_MaxEntryName = 256,

RAS_MaxDeviceName = 128,

RAS_MaxCallbackNumber = RAS_MaxPhoneNumber,

#else

RAS_MaxEntryName = 20,

RAS_MaxDeviceName = 32,

RAS_MaxCallbackNumber = 48,

#endif

RAS_MaxAreaCode = 10,

RAS_MaxPadType = 32,

RAS_MaxX25Address = 200,

RAS_MaxFacilities = 200,

RAS_MaxUserData = 200,

RAS_MaxReplyMessage = 1024,

RAS_MaxDnsSuffix = 256,

UNLEN = 256,

PWLEN = 256,

DNLEN = 15

}

[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Auto)]

public struct RasEntryName

{

public int dwSize;

[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]

public string szEntryName;

[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]

public string szEntryName;

[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

}

 [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
           )
     具体的信息还请参考MSDN，这里更全面，更具有权威性。

ternal enum RasFieldSizeConstants

{

RAS_MaxDeviceType = 16,

RAS_MaxPhoneNumber = 128,

RAS_MaxIpAddress = 15,

RAS_MaxIpxAddress = 21,

#if WINVER4

RAS_MaxEntryName = 256,

RAS_MaxDeviceName = 128,

RAS_MaxCallbackNumber = RAS_MaxPhoneNumber,

#else

RAS_MaxEntryName = 20,

RAS_MaxDeviceName = 32,

RAS_MaxCallbackNumber = 48,

#endif

RAS_MaxAreaCode = 10,

RAS_MaxPadType = 32,

RAS_MaxX25Address = 200,

RAS_MaxFacilities = 200,

RAS_MaxUserData = 200,

RAS_MaxReplyMessage = 1024,

RAS_MaxDnsSuffix = 256,

UNLEN = 256,

PWLEN = 256,

DNLEN = 15

}

[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Auto)]

public struct RasEntryName

{

public int dwSize;

[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]

public string szEntryName;

[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]

public string szEntryName;

[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

}

 [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
           )
     具体的信息还请参考MSDN，这里更全面，更具有权威性。

  在C#下使用API函数不能像VC++那样直接使用，需要进行

  重新声明。而所用到的结构体也要重新定义。VC++中有好

  多数据类型在C#下有不能得到支持，因此在重新定义结构体

  的时候还需要进行数据类型的替换。

  上面提到了RasEnumEntries和RASENTRYNAME。

  它们在C#下的声明和定义如下：

ternal enum RasFieldSizeConstants

{

RAS_MaxDeviceType = 16,

RAS_MaxPhoneNumber = 128,

RAS_MaxIpAddress = 15,

RAS_MaxIpxAddress = 21,

#if WINVER4

RAS_MaxEntryName = 256,

RAS_MaxDeviceName = 128,

RAS_MaxCallbackNumber = RAS_MaxPhoneNumber,

#else

RAS_MaxEntryName = 20,

RAS_MaxDeviceName = 32,

RAS_MaxCallbackNumber = 48,

#endif

RAS_MaxAreaCode = 10,

RAS_MaxPadType = 32,

RAS_MaxX25Address = 200,

RAS_MaxFacilities = 200,

RAS_MaxUserData = 200,

RAS_MaxReplyMessage = 1024,

RAS_MaxDnsSuffix = 256,

UNLEN = 256,

PWLEN = 256,

DNLEN = 15

}

[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Auto)]

public struct RasEntryName

{

public int dwSize;

[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]

public string szEntryName;

[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]

public string szEntryName;

[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

}

 [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
           )
     具体的信息还请参考MSDN，这里更全面，更具有权威性。

ternal enum RasFieldSizeConstants

{

RAS_MaxDeviceType = 16,

RAS_MaxPhoneNumber = 128,

RAS_MaxIpAddress = 15,

RAS_MaxIpxAddress = 21,

#if WINVER4

RAS_MaxEntryName = 256,

RAS_MaxDeviceName = 128,

RAS_MaxCallbackNumber = RAS_MaxPhoneNumber,

#else

RAS_MaxEntryName = 20,

RAS_MaxDeviceName = 32,

RAS_MaxCallbackNumber = 48,

#endif

RAS_MaxAreaCode = 10,

RAS_MaxPadType = 32,

RAS_MaxX25Address = 200,

RAS_MaxFacilities = 200,

RAS_MaxUserData = 200,

RAS_MaxReplyMessage = 1024,

RAS_MaxDnsSuffix = 256,

UNLEN = 256,

PWLEN = 256,

DNLEN = 15

}

[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Auto)]

public struct RasEntryName

{

public int dwSize;

[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]

public string szEntryName;

[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]

public string szEntryName;

[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

}

 [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
           )
     具体的信息还请参考MSDN，这里更全面，更具有权威性。

ternal enum RasFieldSizeConstants

{

RAS_MaxDeviceType = 16,

RAS_MaxPhoneNumber = 128,

RAS_MaxIpAddress = 15,

RAS_MaxIpxAddress = 21,

#if WINVER4

RAS_MaxEntryName = 256,

RAS_MaxDeviceName = 128,

RAS_MaxCallbackNumber = RAS_MaxPhoneNumber,

#else

RAS_MaxEntryName = 20,

RAS_MaxDeviceName = 32,

RAS_MaxCallbackNumber = 48,

#endif

RAS_MaxAreaCode = 10,

RAS_MaxPadType = 32,

RAS_MaxX25Address = 200,

RAS_MaxFacilities = 200,

RAS_MaxUserData = 200,

RAS_MaxReplyMessage = 1024,

RAS_MaxDnsSuffix = 256,

UNLEN = 256,

PWLEN = 256,

DNLEN = 15

}

[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Auto)]

public struct RasEntryName

{

public int dwSize;

[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]

public string szEntryName;

[MarshalAs(UnmanagedType.ByValTStr,SizeConst=(int)RasFieldSizeConstants.RAS_MaxEntryName + 1)]

public string szEntryName;

[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

}

 [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
           )
     具体的信息还请参考MSDN，这里更全面，更具有权威性。