In file included from main.cpp:16:0:
date.h: In function 'std::__cxx11::string FormatString(int, int16_t)':
date.h:5:21: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
     while (capacity != std::to_string(num).length()) {
            ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1plus: all warnings being treated as errors