웹상의 파일 다운로드 및 파일 사이즈 구하는 함수

DWORD GetUrlFileLength (CString url){
	DWORD filesize;

	TCHAR   szCause[255];
	CString CauseOfError;
	TRY{
		CInternetSession session;
		CHttpFile *remotefile= (CHttpFile*)session.OpenURL(url,1,INTERNET_FLAG_TRANSFER_BINARY);
		TCHAR szContentLength[32];
		DWORD dwInfoSize = 32;
		DWORD dwFileSize = 0;
		BOOL bGotFileSize = FALSE;
		if (remotefile->QueryInfo ( HTTP_QUERY_CONTENT_LENGTH, szContentLength, &dwInfoSize , NULL)){
			bGotFileSize = TRUE;
			dwFileSize = (DWORD) _ttol(szContentLength);
			filesize = dwFileSize;// Return 값에 할당.
		}
		else{ // 에러나 나서 파일이 없을경우에 
			filesize = -1 ;
		}
		remotefile->Close ();
		session.Close ();
		delete remotefile;
		delete session;
	}

	CATCH_ALL(error){
		AfxMessageBox ("서버로부터 파일 크기를 얻어오는 과정에서 에러발생");
		error->GetErrorMessage(szCause,254,NULL);
		CauseOfError.Format("%s",szCause);
		AfxMessageBox (CauseOfError);
	}
	END_CATCH_ALL;

	return filesize;
}

위는 파일 사이즈 구하는 함수

void Ca1a1Dlg::DownloadUrlFileBuffer (CString url){
	DWORD dwServiceType = AFX_INET_SERVICE_HTTP;
	CString szServer, szObject, szInfo;

	INTERNET_PORT nPort;
	INTERNET_PROXY_INFO m_proxyinfo;

	CInternetSession m_SessionDownload;
	CHttpConnection* m_pConnection = NULL;
	CHttpFile* m_pHttpFile = NULL;
	CFile FileWrite;

	DWORD d_BytesRead=0;
	DWORD d_FileSize=0;

	char szHTTPBuffer[199926];

	ZeroMemory(szHTTPBuffer, sizeof(szHTTPBuffer));

	//start Download Routine
	::AfxParseURL(url.GetBuffer(url.GetLength()), dwServiceType, szServer, szObject, nPort);

	try{
		m_pConnection = m_SessionDownload.GetHttpConnection(szServer,INTERNET_FLAG_KEEP_CONNECTION, nPort,NULL, NULL);
		m_pHttpFile= m_pConnection->OpenRequest("GET",szObject,NULL,0, NULL, NULL, INTERNET_FLAG_KEEP_CONNECTION);
	}
	catch(CInternetException* m_pException){
		//exception found
		//lots of clean up code
		return;
	}

	if(m_pHttpFile){
		if(!FileWrite.Open("d:\\aaa.gif", CFile::modeCreate | CFile::modeReadWrite | CFile::shareDenyNone )){
			//exception found
			//lots of clean up code
			return;
		}

		try{
			m_pHttpFile->SendRequest(NULL);
		}
		catch(CInternetException* m_pException){
			//exception found
			//lots of clean up code
			return;
		}

		m_pHttpFile->QueryInfo(HTTP_QUERY_CONTENT_LENGTH, d_FileSize);
		m_pHttpFile->QueryInfo(HTTP_QUERY_MAX, szInfo);

		while(d_BytesRead = m_pHttpFile->Read((void*)szHTTPBuffer,199926)){
			FileWrite.Write((void *)szHTTPBuffer,d_BytesRead);
			memset(szHTTPBuffer, 0, sizeof(szHTTPBuffer));
		}

		szServer.Empty();
		szObject.Empty();

		m_SessionDownload.Close();
		m_pConnection->Close();
		m_pHttpFile->Close();

		delete m_SessionDownload;
		delete m_pConnection;
		delete m_pHttpFile;

		FileWrite.Close();
	}
}

출처: http://www.iamgsi.com/entry/MFC-Url-주소에-존재-하는-이미지-다운로드download-받기

이건 파일 다운로드 하는 함수
URLdownloadToFile이랑 차이는 이건 메모리로 직접 읽어들일수 있다 그래서 별도 작업을 할 수 있지.