Check the lask modified, if changed return true;

checkLastModified.h

#include <chrono>
#include <sys/types.h>
#include <sys/stat.h>

std::chrono::time_point<std::chrono::system_clock> lastChangedFileTime;

bool SomeClass::NeedReload
{
  struct stat result;
  if (stat(filePath.c_str(), &result) == 0) {
    auto mod_time = result.st_mtime;
    auto newTime = std::chrono::system_clock::from_time_t(mod_time);
    if (newTime != lastChangedFileTime) {
      lastChangedFileTime = newTime;
      return true;
    }
  }
  return false;
}