createprocess.cpp

#include <windows.h>
#include <filesystem>
#include <iostream>
#include <sstream>
#include <string>

int main(int argc, char* argv[]) {
  // Report command and parameter lengths.
  if (argc > 1) {
    std::cout
      << std::string_view{ argv[0] }.size() << " + "
      << std::string_view{ argv[1] }.size() << std::endl;
    return 0;
  }

  // Get module file name as UTF-8 string.
  DWORD size = 0;
  std::string str;
  do {
    str.resize(str.size() + MAX_PATH);
    size = GetModuleFileName(nullptr, &str[0], static_cast<DWORD>(str.size()));
  } while (GetLastError() == ERROR_INSUFFICIENT_BUFFER);
  str.resize(size);
  const auto m = std::filesystem::canonical(str).string();

  // Create quoted command.
  std::ostringstream oss;
  oss << std::quoted(m) << ' ';
  auto c = oss.str();

  // Generate maximum length parameter.
  c.append(std::string(32'767 - c.size() - 1, 'Q'));

  // Execute command with generated parameter..
  STARTUPINFO si = {};
  si.cb = sizeof(si);
  PROCESS_INFORMATION pi = {};
  CreateProcess(m.data(), c.data(), nullptr, nullptr, TRUE, 0, nullptr, nullptr, &si, &pi);
  WaitForSingleObject(pi.hProcess, INFINITE);
  CloseHandle(pi.hProcess);
  CloseHandle(pi.hThread);
  return 0;
}