CODEWITHSUNDEEP
c#winforms
ChrisPBacon
ChrisPBacon

Reputation: 177

How to append to text file that uses a loop?

My app takes selected information from a SQL database and puts it into a nicely column formatted text file. The problem I have is if the program crashes or stops for any reason, it will overwrite the previous text when restarted.

I'm trying to use the example provided by Microsoft here, but I can't seem to set it up right.

This is the method I'm using to write the text file

private void Output()
    {           
                  string createText = 
                    FormatWidth("Severity", 10) + 
                    FormatWidth("LastNotification", 18) +
                    FormatWidth("FirstNotification", 18) + 
                    FormatWidth("DeviceIP", 18) + 
                    FormatWidth("DeviceInterface", 20) + 
                    "DescriptionShort";

        foreach (KeyValuePair<string, AlarmData> AlarmDataText in AlarmDictionary)
        {
            createText += Environment.NewLine;
            createText += 
            FormatWidth(AlarmDataText.Value.eventSeverity, 8) + 
            FormatWidth(AlarmDataText.Value.eventLastNotification.ToString("yyyy-MM-dd HH:mm"), 18) +
            FormatWidth(AlarmDataText.Value.eventFirstNotification.ToString("yyyy-MM-dd HH:mm"), 18) + 
            FormatWidth(AlarmDataText.Value.deviceIP, 18) + 
            FormatWidth(AlarmDataText.Value.deviceInterface, 20) + 
            AlarmDataText.Value.descriptionShort;
        }

        File.WriteAllText("C:\\Users\\*username*\\Documents\\Visual Studio 2010\\Projects\\NMS_Logger\\NMS_Logger\\bin\\Log.txt", createText);

        Console.WriteLine("File Updated"); //For working verification


    }//end Output()

Upvotes: 1

Views: 2539

Answers (2)

BradleyDotNET
BradleyDotNET

Reputation: 61349

You won't be able to use File.WriteAllText if you want to append, so I would do something like this:

StreamWriter sw;
if (!File.Exists(outputPath)
{
    sw = new StreamWriter(outputPath, false);
    sw.WriteLine(headers);
}
else
    sw = new StreamWriter(outputPath, true);

foreach (...)
   sw.WriteLine(dataLine);

You could initialize the StreamWriter to always append on declaration, but it would have broken the "previous file exists" logic, so I set it up a bit different than usual.

As a side note, you are doing a lot of string concatenation, consider using StringBuilder instead. If you stick with that approach, you could use File.AppendAllText instead of writing each line individually in the foreach. Note that this approach is very memory-inefficient compared to just writing each line to the file (thanks @Servy).

Also, if the program crashes, you'll have a "junk" line in the middle that will be non-trivial to detect (in order to put the newline in). You may want to always insert a new line before you start appending, even though that would cause a weird line break in the data under normal circumstances.

Upvotes: 2

user4237179
user4237179

Reputation:

Check whether file exists before placing the using the c# file exist function or create a new file with different name each time you run the application

Upvotes: 0

Related Questions