如何获取子网掩码

#include <tchar.h>
#include <iphlpapi.h>
#include <stdio.h>
#pragma link "iphlpapi.lib"

void __fastcall TForm1::Button1Click(TObject *Sender)
{
    PMIB_IPADDRTABLE pIPTable = NULL;
    DWORD dwSize = 0;
    ::GetIpAddrTable(pIPTable, &dwSize, TRUE);

    pIPTable = (PMIB_IPADDRTABLE)::GlobalAlloc(GPTR, dwSize);
    ::GetIpAddrTable(pIPTable, &dwSize, TRUE);

    TCHAR szIPAddr[17], szSubMask[17];
    for (DWORD i=0; i < pIPTable->dwNumEntries; i++)
    {
        // IP
        memset(szIPAddr, 0x0, sizeof(szIPAddr));
        _stprintf(szIPAddr, TEXT("%d.%d.%d.%d"),
                LOWORD(pIPTable->table[i].dwAddr) & 0x00FF,
                LOWORD(pIPTable->table[i].dwAddr) >> 8,
                HIWORD(pIPTable->table[i].dwAddr) & 0x00FF,
                HIWORD(pIPTable->table[i].dwAddr) >> 8);

        // Subnet Mask
        memset(szSubMask, 0x0, sizeof(szSubMask));
        _stprintf(szSubMask, TEXT("%d.%d.%d.%d"),
                LOWORD(pIPTable->table[i].dwMask) & 0x00FF,
                LOWORD(pIPTable->table[i].dwMask) >> 8,
                HIWORD(pIPTable->table[i].dwMask) & 0x00FF,
                HIWORD(pIPTable->table[i].dwMask) >> 8);

        Memo1->Lines->Add(String().sprintf(TEXT("IP: %s 子网掩码: %s"),
                szIPAddr, szSubMask));
    }

    ::GlobalFree(pIPTable);
}