How to get a sub-process' return code

Question

What is the method of getting the return value from spawning a sub-process within windows? It looks like ShellExecute() is simpler to use than is CreateProcess(), but from the reading I've done thus far, neither indicate how to check the return value of the spawned process. How is that done?

Thanks, Andy

Answer 1

To acquire the exit code of a process on Windows you can use GetExitCodeProcess().

Example application that accepts the process id as an argument and waits for five seconds for it to complete and then acquires its exit code:

int main(int a_argc, char** a_argv)
{
    int pid = atoi(*(a_argv + 1));

    HANDLE h = OpenProcess(SYNCHRONIZE | PROCESS_QUERY_INFORMATION, FALSE, pid);

    if (NULL != h)
    {
        WaitForSingleObject(h, 5000); // Change to 'INFINITE' wait if req'd
        DWORD exit_code;
        if (FALSE == GetExitCodeProcess(h, &exit_code))
        {
            std::cerr << "GetExitCodeProcess() failure: " <<
                GetLastError() << "\n";
        }
        else if (STILL_ACTIVE == exit_code)
        {
            std::cout << "Still running\n";
        }
        else
        {
            std::cout << "exit code=" << exit_code << "\n";
        }
        CloseHandle(h);
    }
    else
    {
        std::cerr << "OpenProcess() failure: " << GetLastError() << "\n";
    }

    return 0;
}

Answer 2

Here is a complete code based in http://msdn.microsoft.com/en-us/library/windows/desktop/ms682512%28v=vs.85%29.aspx and the solution of hmjd:

#include <stdio.h>
#include <Windows.h>

int main()
{
  const size_t stringSize = 1000;
  STARTUPINFO si;
  PROCESS_INFORMATION pi;
  DWORD exit_code;
  char commandLine[stringSize] = "C:\\myDir\\someExecutable.exe param1 param2";
  WCHAR wCommandLine[stringSize];
  mbstowcs (wCommandLine, commandLine, stringSize);

  ZeroMemory( &si, sizeof(si) );
  si.cb = sizeof(si);
  ZeroMemory( &pi, sizeof(pi) );

  // Start the child process. 
  if( !CreateProcess( NULL,   // No module name (use command line)
      wCommandLine,   // Command line
      NULL,           // Process handle not inheritable
      NULL,           // Thread handle not inheritable
      FALSE,          // Set handle inheritance to FALSE
      0,              // No creation flags
      NULL,           // Use parent's environment block
      NULL,           // Use parent's starting directory 
      &si,            // Pointer to STARTUPINFO structure
      &pi )           // Pointer to PROCESS_INFORMATION structure
  ) 
  {
      printf("CreateProcess failed (%d).\n", GetLastError() );
      return -1;
  }

  // Wait until child process exits.
  WaitForSingleObject( pi.hProcess, INFINITE );

  GetExitCodeProcess(pi.hProcess, &exit_code);

  printf("the execution of: \"%s\"\nreturns: %d\n", commandLine, exit_code);

  // Close process and thread handles. 
  CloseHandle( pi.hProcess );
  CloseHandle( pi.hThread );
  return 0;
}

(runs as VS2005 console application in windows XP)