WinInet basics

Code:

#define WIN32_LEAN_AND_MEAN // exclude rarely-used stuff from windows headers
#include <windows.h> //for winmain/messagebox
#include <wininet.h> //wininet api
#ifdef _MSC_VER //is this a microsoft compiler?
#pragma comment(lib, "wininet.lib") // may not be necessary on non-microsoft compilers; wininet.lib is not included when linking by default on MSVC at least
#endif // _MSC_VER
#include <string> //for retVal in GetPage
using namespace std;

string GetPage(LPCSTR server, LPCSTR path) // LPCSTR is a Win32 type that's equivalent to const char*
//note that you can put this in a static library or a DLL allowing use of it in other projects. the latter option allows it to be used even in non-C++ languages
// --- if you can get around the return type... lol
{
	DWORD dwRead;
	HINTERNET hClient = InternetOpen("GetPage/1.0",INTERNET_OPEN_TYPE_DIRECT,NULL,NULL,0);
	hClient = InternetConnect(hClient,server,INTERNET_DEFAULT_HTTP_PORT,"","",INTERNET_SERVICE_HTTP,0,0);
/* The above two lines are WinInet API calls.  The first creates the HTTP client with the user-agent GetPage/1.0.  The second connects to the HTTP address specified in the second parameter (server). */
	if(!hClient)
	{
		MessageBox(NULL,"An error occured while trying to connect to the host specified.",NULL,MB_OK);
		SetLastError(ERROR_CONNECTION_INVALID);
		return "Error opening site";
	}
/* If the Internet connection failed or the server doesn't exist, then tell the user so and set the last system error to invalid connection.  Useful for debugging. */
	hClient = HttpOpenRequest(hClient,"GET",path,NULL,NULL,NULL,INTERNET_FLAG_KEEP_CONNECTION,0);
/* Uses the HTTP GET command to retrieve the page specified by the parameter following it (replace path with the remote file path, eg "/index.php"). */
/* This is not always the verb you will use; POST is sometimes necessary as well */
	HttpSendRequest(hClient,NULL,0,NULL,0);
// so that hData can be used as a handle to InternetReadFile
	CHAR  pageContents[2048]; //amount read each loop; somewhat arbitrary
	string retVal;
	while(InternetReadFile(hClient,pageContents,255,&dwRead))
	{
		if(dwRead==0) //EOF?
		{
			break; //Quit
		}
		pageContents[dwRead]=0;
		retVal+=pageContents;
// puts the contents into the retVal string and then when the end of the remote file is reached, break and stop.
	}
	
	InternetCloseHandle(hClient);
// free up memory used by the handle you initialized.  after using this function your handle may no longer be used for wininet apis
	return retVal;
//return the string containing the page contents.
}
int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd)
{
	string myIP = GetPage("www.whatismyip.org","/"); //get the index of whatismyip.org
	// note that the actual remote filename is unnecessary for reading the index, just / will do.
	const char *buffer = myIP.c_str(); //convert myIP to a type compatible with MessageBox
	MessageBox(0,buffer,"Your IP is:",MB_OK|MB_ICONINFORMATION); // display IP to user
	return 0;
}

Connects to the simplest plain-text HTTP page I know of and retrieves your IP address for you. I have commented the code extensively and believe it is pretty self-explanatory.

 

Thanks for sharing SMR!