Boost C++ Application Development Cookbook - Second Edition

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What happens in case of an incorrect format?

Nothing awful, an exception is thrown:

    try {        class_instance.to_string("%1% %2% %3% %4% %5%\n");        assert(false);    } catch (const std::exception& e) {        // boost::io::too_few_args exception is catched.        std::cout << e.what() << '\n';    }

The following lines are outputted to the console by the previous code snippet:

 boost::too_few_args: format-string referred to more arguments than    were passed

C++17 has no std::format. The Boost.Format library is not a very fast library. Try not to use it in performance critical sections a lot.