freopen("log.txt", "w", stdout);
cout << "Happy Spring!" << endl;
fclose(stdout);

std::ofstream outFile("log.txt");
outFile << "Happy Spring!" << endl;
outFile.close();

std::ofstream outFile("log.txt");
cout << "Happy Spring!" << endl;
outFile.close();

ofstream log_file("log.txt");
streambuf* org_cout = cout.rdbuf();
cout.rdbuf(log_file.rdbuf());
cout << "Happy Spring!" << endl;
cout.rdbuf(org_cout);