Checking if process returned an error | C#

Question

After declaring & starting a process as below:

System.Diagnostics.Process _p = new System.Diagnostics.Process();
.....
.....
....
_p.Start();

There are two possibilities now: Either an output or an error.

In case an error happens, is there any property of Process class by which to know if error occurred?

I am redirecting the standard output, I don't want to redirect standard Error as warned in MSDN. Also I don't want to use: BeginOutputReadLine();

Are there any alternatives?

Thank you.

Answer 1

I have a service that needs to start processes and wait for them to exit, and I use something like:

process.Start();
int timeout = ... // some normal value in milliseconds

process.WaitForExit(timeout);

try
{
   //ExitCode throws if the process is hanging
   return (CommandErrorCode)process.ExitCode;
}
catch (InvalidOperationException ioex)
{
   return CommandErrorCode.InternalError;
}

where CommandErrorCode is something like

public enum CommandErrorCode
{
    Success = 0,
    //some other values I know from the processes that are managed
    InternalError = 256 // the ExitCode is a byte, so this out of that range
}

Btw, I redirect both standard output and standard error, and use BeginXXXReadLine and the XXXDataReceived handlers, and do not have any issues, but the processes I use are known, well-defined, and well-behaved.

Answer 2

Here is a code snippet , hope this helps

http://ss64.com/nt/cmd.html for cmd.exe help

private int CallShell(string exeCommand, string Parameters)
        {
            //http://ss64.com/nt/cmd.html
            /*
            This function will actually take the shell string and envoke the appropriate process
             passing it the arguments to do the work
            */

            // Initialize the process and its StartInfo properties.
            System.Diagnostics.Process ProcessEXE = new System.Diagnostics.Process();

            logger.DebugFormat("About to Start Process - {0} {1}",exeCommand, Parameters);
            try
            {

                ProcessEXE.StartInfo.FileName = exeCommand;


                // Set UseShellExecute to false for redirection.
                //  false if the process should be created directly from the executable file
                ProcessEXE.StartInfo.UseShellExecute = false;
                ProcessEXE.StartInfo.WorkingDirectory = System.Environment.CurrentDirectory;

                //EnableRaisingEvents property indicates whether the component should be notified when the operating system has shut down a process

                ProcessEXE.StartInfo.Arguments = Parameters;

                ProcessEXE.StartInfo.RedirectStandardOutput = true;
                ProcessEXE.StartInfo.RedirectStandardError = true;
                ProcessEXE.EnableRaisingEvents = true;
                ProcessEXE.StartInfo.CreateNoWindow = true;

                ProcessEXE.OutputDataReceived += new System.Diagnostics.DataReceivedEventHandler(ProcessEXE_OutputDataReceived);
                ProcessEXE.ErrorDataReceived += new System.Diagnostics.DataReceivedEventHandler(ProcessEXE_OutputDataReceived);

                logger.DebugFormat("Process Started.");
                ProcessEXE.Start();


                // Start the asynchronous read of the sort output stream.
                ProcessEXE.BeginErrorReadLine();
                ProcessEXE.BeginOutputReadLine();

                //The WaitForExit overload is used to make the current thread wait until the associated process terminates
                logger.DebugFormat("Process Waiting for exit.");
                ProcessEXE.WaitForExit();

                if (ProcessEXE.ExitCode == 0)
                {
                    logger.Debug(string.Format("Shell Process exited with exit code {0}", ProcessEXE.ExitCode));
                }
                else
                {
                // throw error here if required - check the return error code
                    logger.Warn(string.Format("Shell Process exited with exit code {0}", ProcessEXE.ExitCode));
                }
            }
            catch (Exception ex)
            {
                throw new Exception(string.Format("Method:{0}", ex.TargetSite), ex);
            }

            return ProcessEXE.ExitCode;
        }


void ProcessEXE_OutputDataReceived(object sender, System.Diagnostics.DataReceivedEventArgs e)
        {
            try
            {
                StringBuilder sb = new StringBuilder(string.Empty);
                if (e == null) return;

                if (e.Data == null)
                {
                    //No processing
                }
                else
                {
                   // your logic to detect error msg out from output - if at all required
                }

                if (sb.ToString().ToUpper().IndexOf("ERROR") > 0)
                {
                    string smessage = "Error text found in  output.";

                // do your error response action here .

                }
            }
            catch (Exception exp)
            {
                logger.ErrorFormat("Error in ProcessEXE_OutputDataReceived Message:{0}", exp.Message);
                logger.ErrorFormat("Error in ProcessEXE_OutputDataReceived Data Received:{0}", e.Data);

            // either throw error msg or kill the process 
            }
            finally
            {
                // Not throwing the exception
            }
        }