GetIpForwardTable C++

gistfile1.cpp

#include <winsock2.h>
#include <iphlpapi.h>
#include <cstdio>
#include <memory>

#pragma comment(lib, "iphlpapi.lib")
#pragma comment(lib, "ws2_32.lib")

int main()
{
    std::unique_ptr<MIB_IPFORWARDTABLE> forwardTable;
    ULONG forwardTableSize = 0;
    if (GetIpForwardTable(forwardTable.get(), &forwardTableSize, FALSE) != ERROR_INSUFFICIENT_BUFFER)
    {
        // Handle error
        printf("error1\n");
    }
    forwardTable = std::unique_ptr<MIB_IPFORWARDTABLE>((PMIB_IPFORWARDTABLE)operator new(forwardTableSize));
    if (GetIpForwardTable(forwardTable.get(), &forwardTableSize, FALSE) != NO_ERROR)
    {
        // Handle error
        printf("error2\n");
    }
    // forwardTable is finally valid
    // Now same for ipTable
    std::unique_ptr<MIB_IPADDRTABLE> ipTable;
    ULONG ipTableSize = 0;
    if (GetIpAddrTable(ipTable.get(), &ipTableSize, FALSE) != ERROR_INSUFFICIENT_BUFFER)
    {
        // Handle error
        printf("error1\n");
    }
    ipTable = std::unique_ptr<MIB_IPADDRTABLE>((PMIB_IPADDRTABLE)operator new(ipTableSize));
    if (GetIpAddrTable(ipTable.get(), &ipTableSize, FALSE) != NO_ERROR)
    {
        // Handle error
        printf("error2\n");
    }
    
    for (DWORD i = 0; i < forwardTable->dwNumEntries; i++)
    {
        auto &forwardRow = forwardTable->table[i];
        if (forwardRow.dwForwardDest == 0)
        {
            for (DWORD j = 0; j < ipTable->dwNumEntries; j++)
            {
                auto &ipRow = ipTable->table[j];
                if (ipRow.dwIndex == forwardRow.dwForwardIfIndex)
                {
                    printf("ReturnValue = %08x", ipRow.dwAddr);
                    break;
                }
            }

            break;
        }
    }
    return 0;
}

output:

ReturnValue =  0202a8c0