Why does my StreamWriter overwrite my whole .txt file?

Question

I'm changing a value within my text, but instead, it's overwriting my whole .txt file with nothing.

static void editClassMates(classMates[] classMateInfo)
{
    StreamWriter sw = new StreamWriter(@"C:\Users\Callum\Documents\class.txt");
    Console.Write("Who's number would you like to change? ");
    string classMateInput = Console.ReadLine();
    for (int i = 0; i < classMateInfo.Length; i++)
    {
        if (classMateInfo[i].last.Equals(classMateInput))
        {
            Console.Write("Enter new number: ");
            string temp = Console.ReadLine();
            int classMateNumber = Convert.ToInt32(temp);
            classMateInfo[i].ID = classMateNumber;
        }   
    }
    sw.Close();
}

My code asks for a name within my .txt file. Once I have specified the name, it loops through until my input matches the same exact name in my .txt file. I now want to change his/her number. After I input a number, I then have a method that displays the list and the change I have made. That works, it shows me my original data along with the value I've edited.

However, I go into my class.txt file and it's completely blank now.

My question is, what part of my code is overwriting my whole file? Also, how can I properly change/edit/replace a specific value inside my .txt file?

Thanks

`new StreamWriter(@"C:\Users\Callum\Documents\class.txt", true)` you are not using the overload to append. This is easily viewed in Intellisense as you type — Ňɏssa Pøngjǣrdenlarp, Jun 11 '15 at 12:19
@Plutonix Why don't you put this as an answer? Are you waiting someone to copy-paste it as his own answer? — , Jun 11 '15 at 12:20
Hint: The `File.Open`-Method is even more easy to use. Topic in [this SO article](http://stackoverflow.com/questions/7405828/streamwriter-rewrite-the-file-or-append-to-the-file). @Desolator It's not worth an answer ^.^ — Patrik, Jun 11 '15 at 12:22
@Desolator Well, some people is not interested in reputation points and just want to help others ;-) — Oscar, Jun 11 '15 at 12:22
possible duplicate of [Append lines to a file using a StreamWriter](http://stackoverflow.com/questions/7306214/append-lines-to-a-file-using-a-streamwriter) — Ňɏssa Pøngjǣrdenlarp, Jun 11 '15 at 12:23
@PatrikEckebrecht I am interested in them too :) I put it as a community-wiki answer ! — , Jun 11 '15 at 12:28
@Oscar I am not interested in them too :) I put it as a community-wiki answer ! — , Jun 11 '15 at 12:29
As a side point: you only show code to *open* the file and *close* it, but no code to actually write anything to the file (and since you don't append, your file is empty). — crashmstr, Jun 11 '15 at 12:30
asking which part overwriting the content of the file is okay.. people answered it.. but immediately asking who to read/update/delete value form text file is different. that should be separate one.. — Deepak Sharma, Jun 11 '15 at 12:32
Show us how you are **reading** your file initially, then we can help you with modifying it... — Idle_Mind, Jun 11 '15 at 14:17

score 0 · Answer 1 · edited May 23 '17 at 12:16

0

new StreamWriter(@"C:\Users\Callum\Documents\class.txt", true)

You are not using the overload to append. This is easily viewed in Intellisense as you type.

Hint: The File.Open-Method is even more easy to use. Topic in this SO article

edited May 23 '17 at 12:16

Community

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answered Jun 11 '15 at 12:27

This is not writing to my .txt file. – bsd u Jun 11 '15 at 12:45
See the comments above by @crashmstr – Jun 11 '15 at 12:46
I'm not trying to add a new value to the end. I'm simply trying to edit a value somewhere in between my .txt file. Hence the looping until the correct value is found. Once found, replace their number with my input. I have that set up, but it's really not editing the value at all. – bsd u Jun 11 '15 at 12:52
@bsdu Can your file be large (more than 10MBs)? If no, simple read the entire file in a string, replace values in it as you want, and write this string back to the file. – Jun 11 '15 at 12:56
@bsdu your code posted does not write anything nor read anything! To *change* a file, the simplest way is to write out the whole file with the changes. So in other words: write out every element of `classMateInfo` to your file (`WriteAllLines` is very good for this). – crashmstr Jun 11 '15 at 13:20

Why does my StreamWriter overwrite my whole .txt file?

1 Answers1