simple header only url decoder

urldecode.hpp

#ifndef TEST_DECODE
#pragma once
#else
#include <iostream>
#endif
#include <string>

std::string urldecode(const std::string& url) {
  // make a place for the output
  std::string decoded;
  decoded.reserve(url.size());
  // keep going until we cant go anymore
  size_t pos = 0;
  while (pos < url.size()) {
    // if we can find a percent in the remaining string
    auto next_pos = url.find('%', pos);
    if (next_pos < url.size() - 2) {
      // copy everything up to that point
      decoded.append(url, pos, next_pos - pos);
      // decode it
      auto c =
          static_cast<std::string::value_type>(std::stoi(url.substr(next_pos + 1, 2), nullptr, 16));
      decoded.push_back(c);
      // move pos past the end of what we decoded
      pos = next_pos + 3;
    } // we were done so just get the rest
    else {
      decoded.append(url, pos, url.size() - pos);
      pos = url.size();
    }
  }
  // hand it back
  return decoded;
}

#ifdef TEST_DECODE
int main(int argc, char** argv) {
  std::cout << urldecode(argv[1]) << std::endl;
  return 0;
}
#endif