g++ -std=c++17 md5.cpp -lcryptopp

md5.cpp

#include <crypto++/files.h>
#include <crypto++/hex.h>
#include <crypto++/md5.h>
#include <filesystem>
#include <string>

namespace {

std::string md5(const std::filesystem::path &file) {
  std::string ret;
  CryptoPP::MD5 hash;

  CryptoPP::FileSource f(
      file.c_str(), true,
      new CryptoPP::HashFilter(
          hash, new CryptoPP::HexEncoder(new CryptoPP::StringSink(ret))));

  return ret;
}

} // namespace

int main(int argc, char *argv[]) {
  if (argc < 2) {
    std::cerr << "Usage: md5 file" << std::endl;
    return 1;
  }

  std::cout << argv[1] << ": " << md5(std::filesystem::path{argv[1]})
            << std::endl;
  return 0;
}