Processes: How can I start a process?

[Andreas Masur]

Q: How can I start a process ?

A: There are several ways to start a process:

• 'system()' family (C run-time library - ANSI ('system()') or Win NT ('_wsystem()'))
• '_exec()' family (C run-time library - Win 95, Win NT)
• '_spawn()' family (C run-time library - Win 95, Win NT)
• 'WinExec()' (Win32 API)
• 'ShellExecute()' (Shell API)
• 'ShellExecuteEx()' (Shell API)
• 'CreateProcess()' (Win32 API)
• 'CreateProcessAsUser()' (Win32 API)
• 'CreateProcessWithLogonW()' (Win32 API)

Most common are 'ShellExecute()', ShellExecuteEx()' and 'CreateProcess()'. Note that 'WinExec()' is provided only for compatibility with 16-bit Windows and should not be used any longer. The following examples will show how to display the text file 'c:\example.txt' in 'notepad.exe' using these three functions...

• 'ShellExecute()'
  

      HINSTANCE hInst = ShellExecute(0,                           
                                     "open",                      // Operation to perform
                                     "c:\\windows\\notepad.exe",  // Application name
                                     "c:\\example.txt",           // Additional parameters
                                     0,                           // Default directory
                                     SW_SHOW);
      if(reinterpret_cast<int>(hInst) <= 32)
      {
        // Could not start application
        switch(reinterpret_cast<int>(hInst))
        {
          case 0:
            // The operating system is out of memory or resources.
            break;
  
          case ERROR_FILE_NOT_FOUND:
            // The specified file was not found.
            break;
  
          case ERROR_PATH_NOT_FOUND:
            // The specified path was not found.
            break;
  
          case ERROR_BAD_FORMAT:
            // The .exe file is invalid (non-Microsoft Win32 .exe or error in .exe image).
            break;
  
          case SE_ERR_ACCESSDENIED:
            // The operating system denied access to the specified file.
            break;
  
          case SE_ERR_ASSOCINCOMPLETE:
            // The file name association is incomplete or invalid.
            break;
  
          case SE_ERR_DDEBUSY:
            // The Dynamic Data Exchange (DDE) transaction could not be completed because
            // other DDE transactions were being processed.
            break;
  
          case SE_ERR_DDEFAIL:
            // The DDE transaction failed.
            break;
  
          case SE_ERR_DDETIMEOUT:
            // The DDE transaction could not be completed because the request timed out.
            break;
  
          case SE_ERR_DLLNOTFOUND:
            // The specified dynamic-link library (DLL) was not found.
  
          case SE_ERR_FNF:
            // The specified file was not found.
            break;
  
          case SE_ERR_NOASSOC:
            // There is no application associated with the given file name extension.
            // This error will also be returned if you attempt to print a file that is
            // not printable.
            break;
  
          case SE_ERR_OOM:
            // There was not enough memory to complete the operation.
            break;
  
          case SE_ERR_PNF:
            // The specified path was not found.
            break;
  
          case SE_ERR_SHARE:
            // A sharing violation occurred.
            break;
        }
      }

• 'ShellExecuteEx()'
  

      SHELLEXECUTEINFO ExecuteInfo;
      
      memset(&ExecuteInfo, 0, sizeof(ExecuteInfo));
      
      ExecuteInfo.cbSize       = sizeof(ExecuteInfo);
      ExecuteInfo.fMask        = 0;                
      ExecuteInfo.hwnd         = 0;                
      ExecuteInfo.lpVerb       = "open";                      // Operation to perform
      ExecuteInfo.lpFile       = "c:\\windows\\notepad.exe";  // Application name
      ExecuteInfo.lpParameters = "c:\\example.txt";           // Additional parameters
      ExecuteInfo.lpDirectory  = 0;                           // Default directory
      ExecuteInfo.nShow        = SW_SHOW;
      ExecuteInfo.hInstApp     = 0;
      
      if(ShellExecuteEx(&ExecuteInfo) == FALSE)
        // Could not start application -> call 'GetLastError()'

• 'CreateProcess()'
  

      STARTUPINFO         siStartupInfo;
      PROCESS_INFORMATION piProcessInfo;
  
      memset(&siStartupInfo, 0, sizeof(siStartupInfo));
      memset(&piProcessInfo, 0, sizeof(piProcessInfo));
  
      siStartupInfo.cb = sizeof(siStartupInfo);
  
      if(CreateProcess("c:\\windows\\notepad.exe",     // Application name
                       " example.txt",                 // Application arguments
                       0,
                       0,
                       FALSE,
                       CREATE_DEFAULT_ERROR_MODE,
                       0,
                       0,                              // Working directory
                       &siStartupInfo,
                       &piProcessInfo) == FALSE)
        // Could not start application -> call 'GetLastError()'

In general 'ShellExecuteEx()' and even 'CreateProcess()' provides more controlling features of the application to start and its termination as shown in the FAQ 'How can I wait until a process ends?'