CODEWITHSUNDEEP
c#stringcsvfilestream
hbk
hbk

Reputation: 11184

How to update lines in a CSV file?

I'm trying to update some part of a string in a file. Currently my code is:

FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read);
StreamReader sr = new StreamReader(filePath);

string[] line = sr.ReadToEnd().Split(new string[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries);
List<string> lines = new List<string>();

string eventName = ','+eventNameUpdateTextBox.Text.ToString()+',';
foreach (var l in line)
{
    if (l.Contains(eventName))
    {
        int start = l.IndexOf(eventName);
        l.Remove(start, eventName.Length);
        l.Insert(start, newNameTextBox.Text.ToString());
        lines.Add(l);
    }
    else
    {
        lines.Add(l);
    }   
}

string toCsvOutput = string.Join(Environment.NewLine, lines.ToArray());

But the result I'm getting is the same file as before.
When I try to debug it, I see that function:

  l.Insert(start, newNameTextBox.Text.ToString());

Does not change string and returns the same string as at the beginning. Why does this happen? Where am I wrong?

Upvotes: 2

Views: 2350

Answers (3)

user2480047
user2480047

Reputation:

You have to assign the changes to a new (string) variable. This string variable cannot be l because is the one being iterated in the foreach loop and thus cannot be changed. You have to rely on a temporary variable, as shown in the code below.

foreach (var l in line)
{
    if (l.Contains(eventName))
    {
        string temp = l;
        int start = l.IndexOf(eventName);
        temp = temp.Remove(start, eventName.Length);
        temp = temp.Insert(start, newNameTextBox.Text.ToString());
        lines.Add(temp);
    }
    else
    {
        lines.Add(l);
    }
}

Upvotes: 1

No Idea For Name
No Idea For Name

Reputation: 11577

function on strings return the result strings, but do not change the value of the string(most of them if not all)

try this:

    FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read);
    StreamReader sr = new StreamReader(filePath);

    string[] line = sr.ReadToEnd().Split(new string[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries);
    List<string> lines = new List<string>();

    string eventName = ','+eventNameUpdateTextBox.Text.ToString()+',';
    foreach (var l in line)
    {
        if (l.Contains(eventName))
        {
            int start = l.IndexOf(eventName);
            l = l.Remove(start, eventName.Length);
            l = l.Insert(start, newNameTextBox.Text.ToString());
            lines.Add(l);
        }
        else
        {
            lines.Add(l);
        }   
    }
    string toCsvOutput = string.Join(Environment.NewLine, lines.ToArray());

Upvotes: 1

Tim Schmelter
Tim Schmelter

Reputation: 460058

Strings are immutable, that means they cannot change. You need to create a new string and assign this to the variable.

l = l.Remove(start, eventName.Length);
l = l.Insert(start, newNameTextBox.Text.ToString());

MSDN:

Strings are immutable--the contents of a string object cannot be changed after the object is created, although the syntax makes it appear as if you can do this.

Why .NET String is immutable?

Upvotes: 2

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