Why WSAStartup couldn't get the localhost ip address

[Beon]

Hi everyone,
I had used the WSAStartup & gethostbyname to get a list of ipaddress from the local machine. However the ipaddress for the local host was not shown, Is there anyway retrieve all the usable ipaddress which include the local host? and why is it not shown using WSAData?

[cilu]

Can you show as the code that you used?

[Beon]

Hi my code are as below, I was wondering is there anyway to retrieve the local address too, e.g localhost 127.0.0.1

char ac[80];
struct in_addr addr;      
 

WSAData wsaData;

 

 //Initialize structure
 memset(&addr,0,sizeof(addr));
 memset(&wsaData,0,sizeof(wsaData));
 
 //Specify the version of Windows Sockets 
    if (WSAStartup(MAKEWORD(1, 1), &wsaData) != 0) {
        return false;
    }
 
 //Getting the standard host name for the local machine
    if (gethostname(ac, sizeof(ac)) == SOCKET_ERROR) {
        return false;
    }

 //Retrieving host information corresponding to a host name
 struct hostent *phe = gethostbyname(ac);
    if (phe == FAILURE){
        return false;
    }
 
 //Retrieving list of addresses for the host
    for (int i = 0; phe->h_addr_list != 0; ++i){
        memcpy(&addr, phe->h_addr_list, sizeof(struct in_addr));
    }

 

 WSACleanup();

return true;

[miteshpandey]

Hi,

You can use WSAGetLastError to determine the exact error you are receiving.

[Beon]

Hi miteshpandey,
I don' t think thre is anything wrong with the code, so I dun really need WSAGetLastError to find the error, however I do want to know is there anyway that I can retrieve ip address that with the the local host address included? I had tried to use winsock to find the ip address but it doesn't include the local ip 127.0.0.1 and IP helper is having the same problems. Therefore is there a way to get all the ip which include the local host address?

[miteshpandey]

Not 100% sure but since local host is always 127.0.0.1 it may have been thought redundant to be retrieved by the function. If you are using a list to store the ip addresses, then you can just add 127.0.0.1 as hard coded entry.

[cilu]

I had used the WSAStartup & gethostbyname to get a list of ipaddress from the local machine.

But you should be using GetAdaptersInfo() or GetAdaptersAddresses().

[Beon]

Hi miteshpandey,
Are you sure that the local Ip is always 127.0.0.1? If I remember correctly the reserved IPv4 address block for loopback is 127.0.0.0/8, therefore is it really ok to hardcode the localhost address?

Hi Cilu,
Do you have any examples or links on the GetAdaptersInfo() or GetAdaptersAddresses() for c++,Vs6 as I only manage to find it on c#.

[cilu]

Well, did you take a look in MSDN?

http://msdn2.microsoft.com/en-us/library/aa365917.aspx

[olivthill]

The list of IP addresses that you are retrieving are those that are listed in your .hosts file. There can be several other IP addresses that can be reached from your computer, and that are not listed in this file.

The localhost IP usually is 127.0.0.1. There is a little difference with 127.0.0/8. See http://en.wikipedia.org/wiki/Localhost

A computer can have more than one IP address. Your computer has the 127.0.0.1 address and also another one if it is in a network.

[DennisVM-D2i]

One IP 'loopback'/localhost address might be sufficient, but you might possibly want to use a different one other than the standard one of '127.0.0.1' (- at least if this is for a special/specific usage); this is where IPv6 is a downgrade (/sucks in comparison to IPv4) as it only has one loopback address. ;/

You might be looking for something like this:

// DVM: S: Add loopback adapter

auto currIpAdapterInfo = m_pInfo;
IP_ADAPTER_INFO* parentIpAdapterInfo = nullptr;

while (currIpAdapterInfo != nullptr)
{
parentIpAdapterInfo =
currIpAdapterInfo;

currIpAdapterInfo =
currIpAdapterInfo->Next;
}

// ReSharper disable once CppLocalVariableMayBeConst
bool addLoopbackAdapter = true;

if (addLoopbackAdapter &&
parentIpAdapterInfo != nullptr)
{
IP_ADAPTER_INFO* loopbackIpAdapterInfo =
new IP_ADAPTER_INFO;

loopbackIpAdapterInfo->Next = nullptr;

loopbackIpAdapterInfo->ComboIndex = 999;

strcpy(loopbackIpAdapterInfo->AdapterName, _T("Loopback"));

strcpy(loopbackIpAdapterInfo->Description, _T("Loopback Pseudo-Interface"));

// Hw address length
loopbackIpAdapterInfo->AddressLength = 6;

// Hw address
// 2, 0, 76, 79, 79, 80, 0, 0 - '\x2', '\0', "LOOP", '\0', '\0'
//memset(loopbackIpAdapterInfo->Address, 0, sizeof(loopbackIpAdapterInfo->Address));

loopbackIpAdapterInfo->Address[0] = '\x2';
loopbackIpAdapterInfo->Address[1] = '\0';
loopbackIpAdapterInfo->Address[2] = 127;
loopbackIpAdapterInfo->Address[3] = 4;
loopbackIpAdapterInfo->Address[4] = 0;
loopbackIpAdapterInfo->Address[5] = 2;
loopbackIpAdapterInfo->Address[6] = 0;
loopbackIpAdapterInfo->Address[7] = 0;

//loopbackIpAdapterInfo->Address[0] = '\x2';
//loopbackIpAdapterInfo->Address[1] = '\0';
//loopbackIpAdapterInfo->Address[2] = 'L';
//loopbackIpAdapterInfo->Address[3] = 'O';
//loopbackIpAdapterInfo->Address[4] = 'O';
//loopbackIpAdapterInfo->Address[5] = 'P';
//loopbackIpAdapterInfo->Address[6] = '\0';
//loopbackIpAdapterInfo->Address[7] = '\0';

loopbackIpAdapterInfo->Index = 21; // ???
loopbackIpAdapterInfo->Type = 71; // ??
loopbackIpAdapterInfo->DhcpEnabled = 0;
loopbackIpAdapterInfo->CurrentIpAddress = nullptr;

loopbackIpAdapterInfo->IpAddressList.Next = nullptr;
strcpy(loopbackIpAdapterInfo->IpAddressList.IpAddress.String, _T("127.4.0.2"));
strcpy(loopbackIpAdapterInfo->IpAddressList.IpMask.String, _T("0.0.0.0"));
loopbackIpAdapterInfo->IpAddressList.Context = 0;

loopbackIpAdapterInfo->GatewayList.Next = nullptr;
strcpy(loopbackIpAdapterInfo->GatewayList.IpAddress.String, _T("0.0.0.0"));
strcpy(loopbackIpAdapterInfo->GatewayList.IpMask.String, _T("255.255.255.255"));
loopbackIpAdapterInfo->GatewayList.Context = 0;

loopbackIpAdapterInfo->DhcpServer.Next = nullptr;
loopbackIpAdapterInfo->DhcpServer.IpAddress.String[0] = '\0';
loopbackIpAdapterInfo->DhcpServer.IpMask.String[0] = '\0';
loopbackIpAdapterInfo->DhcpServer.Context = 0;

loopbackIpAdapterInfo->HaveWins = 0;

loopbackIpAdapterInfo->PrimaryWinsServer.Next = nullptr;
loopbackIpAdapterInfo->PrimaryWinsServer.IpAddress.String[0] = '\0';
loopbackIpAdapterInfo->PrimaryWinsServer.IpMask.String[0] = '\0';
loopbackIpAdapterInfo->PrimaryWinsServer.Context = 0;

loopbackIpAdapterInfo->SecondaryWinsServer.Next = nullptr;
loopbackIpAdapterInfo->SecondaryWinsServer.IpAddress.String[0] = '\0';
loopbackIpAdapterInfo->SecondaryWinsServer.IpMask.String[0] = '\0';
loopbackIpAdapterInfo->SecondaryWinsServer.Context = 0;

loopbackIpAdapterInfo->LeaseObtained = 0;
loopbackIpAdapterInfo->LeaseExpires = 103188859728;

parentIpAdapterInfo->Next = loopbackIpAdapterInfo;
}

// DVM: E: Add loopback adapter

[VictorN]

...
You might be looking for something like this:
...

Please, use CODE tags (not the QUOTE ones!) while posting your code snippets. Also don't forget to properly format your code.
Otherwise is looks absolutely unreadable.

[DennisVM-D2i]

The same post again, but as the editor did not seem to have a 'CODE' button, attempting to manually use CODE tags:

//  E.g.  For '127.4.0.2' (- as IPv4 'loopback'/localhost addresses are a class - Class A, '127.4.0.2' being one of them / a valid 'loopback'/localhost address; IPv6 should have reserved at least 10 'loopback'/localhost addresses instead of just the one  =S):

#include "Iphlpapi.h"
#include "Ipifcons.h"

...

                // DVM: B:  Add loopback adapter

                // ReSharper disable once CppLocalVariableMayBeConst
                bool addLoopbackAdapter = true;

                if (addLoopbackAdapter)
                {
                    auto currIpAdapterInfo = m_pInfo;
                    IP_ADAPTER_INFO* parentIpAdapterInfo = nullptr;

                    while (currIpAdapterInfo != nullptr)
                    {
                        parentIpAdapterInfo =
                            currIpAdapterInfo;

                        currIpAdapterInfo =
                            currIpAdapterInfo->Next;
                    }

                    if (parentIpAdapterInfo != nullptr)
                    {
                        const auto loopbackIpAdapterInfo =
                            new IP_ADAPTER_INFO;

                        loopbackIpAdapterInfo->Next = nullptr;

                        loopbackIpAdapterInfo->ComboIndex = 999;

                        strcpy(loopbackIpAdapterInfo->AdapterName, _T("Loopback"));

                        strcpy(loopbackIpAdapterInfo->Description, _T("Loopback Pseudo-Interface"));

                        // Hw address length
                        loopbackIpAdapterInfo->AddressLength = 6;

                        // Hw address
                        // 2, 0, 76, 79, 79, 80, 0, 0 - '\x2', '\0', "LOOP", '\0', '\0'
                        //memset(loopbackIpAdapterInfo->Address, 0, sizeof(loopbackIpAdapterInfo->Address));

                        loopbackIpAdapterInfo->Address[0] = '\x2';
                        loopbackIpAdapterInfo->Address[1] = '\0';
                        loopbackIpAdapterInfo->Address[2] = 127;
                        loopbackIpAdapterInfo->Address[3] = 4;
                        loopbackIpAdapterInfo->Address[4] = 0;
                        loopbackIpAdapterInfo->Address[5] = 2;
                        loopbackIpAdapterInfo->Address[6] = 0;
                        loopbackIpAdapterInfo->Address[7] = 0;

                        //loopbackIpAdapterInfo->Address[0] = '\x2';
                        //loopbackIpAdapterInfo->Address[1] = '\0';
                        //loopbackIpAdapterInfo->Address[2] = 'L';
                        //loopbackIpAdapterInfo->Address[3] = 'O';
                        //loopbackIpAdapterInfo->Address[4] = 'O';
                        //loopbackIpAdapterInfo->Address[5] = 'P';
                        //loopbackIpAdapterInfo->Address[6] = '\0';
                        //loopbackIpAdapterInfo->Address[7] = '\0';

                        loopbackIpAdapterInfo->Index = 99;  // ???
                        loopbackIpAdapterInfo->Type = IF_TYPE_ETHERNET_CSMACD;
                        loopbackIpAdapterInfo->DhcpEnabled = 0;
                        loopbackIpAdapterInfo->CurrentIpAddress = nullptr;

                        loopbackIpAdapterInfo->IpAddressList.Next = nullptr;
                        strcpy(loopbackIpAdapterInfo->IpAddressList.IpAddress.String, _T("127.4.0.2"));
                        strcpy(loopbackIpAdapterInfo->IpAddressList.IpMask.String, _T("0.0.0.0"));
                        loopbackIpAdapterInfo->IpAddressList.Context = 0;

                        loopbackIpAdapterInfo->GatewayList.Next = nullptr;
                        strcpy(loopbackIpAdapterInfo->GatewayList.IpAddress.String, _T("0.0.0.0"));
                        strcpy(loopbackIpAdapterInfo->GatewayList.IpMask.String, _T("255.255.255.255"));
                        loopbackIpAdapterInfo->GatewayList.Context = 0;

                        loopbackIpAdapterInfo->DhcpServer.Next = nullptr;
                        loopbackIpAdapterInfo->DhcpServer.IpAddress.String[0] = '\0';
                        loopbackIpAdapterInfo->DhcpServer.IpMask.String[0] = '\0';
                        loopbackIpAdapterInfo->DhcpServer.Context = 0;

                        loopbackIpAdapterInfo->HaveWins = 0;

                        loopbackIpAdapterInfo->PrimaryWinsServer.Next = nullptr;
                        loopbackIpAdapterInfo->PrimaryWinsServer.IpAddress.String[0] = '\0';
                        loopbackIpAdapterInfo->PrimaryWinsServer.IpMask.String[0] = '\0';
                        loopbackIpAdapterInfo->PrimaryWinsServer.Context = 0;

                        loopbackIpAdapterInfo->SecondaryWinsServer.Next = nullptr;
                        loopbackIpAdapterInfo->SecondaryWinsServer.IpAddress.String[0] = '\0';
                        loopbackIpAdapterInfo->SecondaryWinsServer.IpMask.String[0] = '\0';
                        loopbackIpAdapterInfo->SecondaryWinsServer.Context = 0;

                        loopbackIpAdapterInfo->LeaseObtained = 0;
                        loopbackIpAdapterInfo->LeaseExpires = 103188859728;

                        parentIpAdapterInfo->Next = loopbackIpAdapterInfo;
                    }
                }

                // DVM: E:  Add loopback adapter