Log file in C#

mrithula8

Hi I have listed and then started all the exe files.As and when the exe starts a log file should be maintained which will contain the start time of the exe.So i used the following code.It gives" NullException Object reference not set to an instance of an object" for the following line

stw1.WriteLine("UdpServer at port 10000 has started at:", start1.ToString());

if (cb.Checked)
{
n1 = lb4.Text;
// System.Diagnostics.Process.Start(n1);
si1 = new ProcessStartInfo(n1);
proc = Process.Start(si1);
proclist.Add(proc);

            DateTime start1 = proc.StartTime;
            if (!File.Exists("startlog1.txt"))
            {
                stw1 = new StreamWriter("startlog1.txt");
            }
            else
            {
                File.AppendText("startlog1.txt");
            }
            stw1.WriteLine("UdpServer at port 10000 has started at:", start1.ToString());
            stw1.WriteLine("=======================================================================");
            stw1.Flush();
        }

        if (cb1.Checked)
        {
            n2 = lb5.Text;
            //System.Diagnostics.Process.Start(n2);
            ProcessStartInfo si2 = new ProcessStartInfo(n2);
            proc = Process.Start(si2);
            proclist.Add(proc);

            DateTime start2 = proc.StartTime;
            if (!File.Exists("startlog2.txt"))
            {
                stw2 = new StreamWriter("startlog2.txt");
            }
            else
            {
                File.AppendText("startlog2.txt");
            }
           
            stw2.WriteLine("UdpServer at port 10001 has started at:", start2.ToString());
            stw2.WriteLine("=======================================================================");
            stw2.Flush();

        }

Luc Pattyn

Hi, how many ways are there for stw1.WriteLine("UdpServer...", start1.ToString()); to cause a NullReferenceException? has each of the relevant objects been assigned a value for all possible ways to reach this statement? :)

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mrithula8

Hi Im not able to get you.Can you please explain me how i can write the start time of the corresponding servers to a text file?

Luc Pattyn

Hi, you have the code to do that, however it contains a minor mistake. I gave you the logic steps to pinpoint the mistake. if this is your code, you will have no trouble fixing it. if it is not, you probably won't understand the code, hence be unable to fix it. :)

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King Julien

Hi... The best overloaded method for WriteLine() with two arguments are WriteLine(string,object) and WriteLine(string,object[]) But your method call supplies both the arguments as string... soo doo something like this...

string logString = "Started time: " + start1.ToString();
stw1.WriteLine(logString);

This may help i believe...

Have a Happy Coding.....

Colin Angus Mackay

You are still using the objects start1 and stw1. One (or both) are null. Your code by itself will not solve this error.

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Colin Angus Mackay

mrithula8 wrote:

Can you please explain me how i can write the start time of the corresponding servers to a text file?

He gave you the steps to work it out by yourself. In more detail he means that your code has two possible ways for a NullReferenceException to be raised.

stw1.WriteLine("UdpServer at port 10000 has started at:", start1.ToString());

Either stw1 is null or start1 is null. You must find out why they are null and ensure they have a value or not run that line of code. Once you have solved that you will find that the output is not what you expect. The value of start1 is not output as you have not included a placeholder for it in the text. The text string should probably read something like this:

"UdpServer at port 10000 has started at: {0}"

Note the addition of the {0}

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Colin Angus Mackay

Here is a hint:

if (!File.Exists("startlog1.txt"))
{
stw1 = new StreamWriter("startlog1.txt");
}
else
{
File.AppendText("startlog1.txt");
}

What are you doing when the file exists vs. when the file does not exist? What is the value of stw1 after this if statement in the two scenarios.

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King Julien

Hi Colin..... I dont get you... i just used the string value logString to be passed to the stream writer..... Why do you say it will not solve the problem??? suggest...

Have a Happy Coding.....

Colin Angus Mackay

King Julien wrote:

i just used the string value logString to be passed to the stream writer.....

True, but all you did was move the original posters problem onto a different line of code. You moved his problem on to the line of code that generates the content for logString. The OP's problem was a NullReferenceException. Your code will still produce a NullReferenceException for the reasons I gave in my previous post.

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