How do I find out a public IP address on the Internet using the Win32 API?

Participant 41

I am interested in the public ip address, not the IP address of the local network. Interested in IPv4 and IPv6.

Now I find out my ip address like this: I go to some site that determines the ip address, and the site tells me my ip address. I need to do this using the Win32 API.

I am interested in the Win32 API, and not any programming languages (C++, C#, etc.).

RLWA32 45,476 Reputation points

2024-06-24T08:56:56.8+00:00

Is your system connected directly to the internet or is it behind a router?
David Lowndes 2,535 Reputation points MVP

2024-06-24T11:28:30.45+00:00

Assuming your PC is behind a router, I think you'd need to use a service such as api.ipify.org - https://www.ipify.org/.

Accepted answer

Castorix31 85,116

Yes, you need to use an external website.

For example with Wininet on my PC :

					HINTERNET hInternet = InternetOpen(NULL, INTERNET_OPEN_TYPE_PRECONFIG_WITH_NO_AUTOPROXY, NULL, NULL, 0);
					if (hInternet != NULL)
					{
						HINTERNET hFile = InternetOpenUrl(hInternet, _T("https://api.ipify.org"), NULL, 0, INTERNET_FLAG_RELOAD, 0);
						if (hFile != NULL)
						{
							CHAR sBuffer[MAX_PATH];
							TCHAR wsBuffer[MAX_PATH];
							DWORD nRead;
							BOOL bRet = InternetReadFile(hFile, sBuffer, sizeof(sBuffer), &nRead);
							if (bRet)
							{
								sBuffer[nRead] = '\0';
								MultiByteToWideChar(CP_ACP, 0, sBuffer, -1, wsBuffer, MAX_PATH);
								TCHAR wsMessage[MAX_PATH] = _T("");
								wsprintf(wsMessage, _T("External IP : %s"), wsBuffer);
								MessageBox(NULL, wsMessage, _T("Information"), MB_OK | MB_ICONINFORMATION);
							}
							InternetCloseHandle(hFile);							
						}
						InternetCloseHandle(hInternet);
					}

7 additional answers

David Lowndes 2,535 MVP

You just need to do a Http get operation. Here's an example:

static LPCWSTR AcceptTypes[]{ L"text/*", NULL };

static std::string GetIPAddressFromService()
{
	std::string sMyPublicAddress;
	unique_HINTERNET hOpen{ InternetOpen( L"", INTERNET_OPEN_TYPE_PRECONFIG, NULL, NULL, 0 ) };
	if ( hOpen != NULL )
	{
		unique_HINTERNET hConn{ InternetConnect( hOpen.get(), L"api.ipify.org", INTERNET_DEFAULT_HTTPS_PORT, NULL, NULL, INTERNET_SERVICE_HTTP, 0, 1 ) };
		if ( hConn != NULL )
		{
			// Try 3x before giving up so as not to wait excessively
			for ( int rcnt = 0; (rcnt < 3) && sMyPublicAddress.empty(); ++rcnt )
			{
				// GET is the default; use https
				unique_HINTERNET hReq{ HttpOpenRequest( hConn.get(), NULL, L"", NULL, NULL, AcceptTypes, INTERNET_FLAG_NO_UI | INTERNET_FLAG_SECURE, 1 ) };
				if ( hReq != NULL )
				{
					if ( HttpSendRequest( hReq.get(), NULL, 0, NULL, 0 ) )
					{
						// The expected response is the IP (v4) address as a string
						char ipAddrStr[sizeof( "255.255.255.255" )];
						DWORD BytesRead;
						if ( InternetReadFile( hReq.get(), ipAddrStr, sizeof( ipAddrStr ), &BytesRead ) )
						{
							sMyPublicAddress = std::string( ipAddrStr, BytesRead );
							// Check what we have is an ipv4 address by converting it
							IN_ADDR inaddr;
							int rv = inet_pton( AF_INET, sMyPublicAddress.c_str(), &inaddr );
							// 1 means OK!
							if ( rv != 1 )
							{
								// We got an invalid string for the address, clear it and retry
								sMyPublicAddress.clear();
							}
						}
					}
				}
			}
		}
	}
	return sMyPublicAddress;
}

Xiaopo Yang - MSFT 12,726 Reputation points Microsoft Vendor

2024-06-24T08:04:14.6666667+00:00

Hello @Participant, A way is GetAdaptersAddresses(). Also see the question as a result of quick search.
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Participant 41 Reputation points

2024-06-24T08:49:53.51+00:00

XiaoYang - MSFT, the link you provided discusses the topic: How to get the local IP address of Windows system? Pay attention to "local". I use the term "public" in my first post. Be careful when you give advice.

Since you do not see the difference between "local" and "public", I assume that the "GetAdaptersAddresses" function you proposed will not give the desired result.
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Participant 41 Reputation points

2024-06-24T13:02:43.43+00:00

RLWA32, I'm accessing the Internet through a router.

David Lowndes, are you suggesting using the Win32 API or a website that will tell me my ip address?
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David Lowndes 2,535 Reputation points MVP

2024-06-24T13:22:21.4366667+00:00

The latter - I'm suggesting that you write code to get the address from a web service.

RLWA32 45,476 Reputation points

2024-06-24T13:25:22.18+00:00

RLWA32, I'm accessing the Internet through a router.

That's what I expected. Windows API functions will return the IP addresses that were provided to your system by the router (either DHCP or static depending on your particular configuration). The "public" IP address returned by an internet service is the one that is accessible to the router, not the Windows systems behind it.
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How do I find out a public IP address on the Internet using the Win32 API?

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