파일 존재하는지 체크

https://stackoverflow.com/questions/12774207/fastest-way-to-check-if-a-file-exists-using-standard-c-c11-14-17-c

path가 파일인지 디렉토리인지 체크

• C++98
  • https://www.codegrepper.com/code-examples/cpp/how+to+find+out+if+a+directory+exists+in+cpp
• C++17
  • https://en.cppreference.com/w/cpp/filesystem/file_type