直接上程式碼，呵呵！

//獲取公網ip
#include <urlmon.h>
#pragma comment(lib, "urlmon.lib")

#ifdef _UNICODE
#define tString std::wstring
#else
#define tString std::string
#endif

//----------獲取客戶端公網IP-----------//
tString GetIP()
{
	TCHAR szPath[MAX_PATH] = { 0 };
	TCHAR szRead[128] = { 0 };

	char szSite[] = "http://www.3322.org/dyndns/getip";

	GetTempPath(MAX_PATH, szPath);
	_tcscat_s(szPath, 256, _T("get_ip.txt"));

	if (URLDownloadToFile(0, szSite, szPath, 0, 0) == S_OK)
	{
		FILE *fIpHtm;

		if (fopen_s(&fIpHtm, szPath, "r") == S_OK && fIpHtm)
		{
			fgets(szRead, 128, fIpHtm);
		}
	}

	return tString(szRead);
}


int _tmain(int argc, _TCHAR* argv[])
{
	_tprintf(_T("\nget net ip!\n"));
	_tprintf(_T("%s\n"), GetIP().c_str());

	getchar();

	return 0;
}