Automatically recompile c++ file when the source changes

rebuild.hpp

#include <cstdlib>
#include <filesystem>

#ifndef LAST_BUILD
#define LAST_BUILD 0
#endif

// USAGE:
// ```cpp
// int main(int argc, char** argv) {
//     REBUILD(argc, argv);
//     // actual work
//     return 0;
// }
// ```
#define REBUILD(argc, argv)                                                    \
  {                                                                            \
    auto last_write = std::filesystem::last_write_time(__FILE__);              \
    auto last_write_unix = last_write.time_since_epoch().count();              \
    if (last_write_unix != LAST_BUILD) {                                       \
      std::stringstream ss;                                                    \
      ss << "c++ " << __FILE__ << " -o " << argv[0] << " -std=c++"             \
         << __cplusplus / 100 % 100 << " -DLAST_BUILD=" << last_write_unix     \
         << '\n';                                                              \
      if (std::system(ss.str().c_str()))                                       \
        return 1;                                                              \
      std::system(argv[0]);                                                    \
      return 0;                                                                \
    }                                                                          \
  }