Question

I’m reading a file using C# and class TextReader

TextReader reader = new StreamReader(stream);
string line;
while ((line = reader.ReadLine()) != null)
 {
   if (someCondition)
    {
      // I want to change "line" and save it into the file I'm reading from
    }
 }

In a code there is a question: how do I save a changed line to a file I’m reading from and continue reading?

Answer 1

Fast and dirty solution would be:

TextReader reader = new StreamReader(stream);
string line;
StringBuilder sb = new StringBuilder();
while ((line = reader.ReadLine()) != null)
{
    if (someCondition)
    {
       //Change variable line as you wish.
    }
    sb.Append(line);
 }

using (StreamWriter sw = new StreamWriter("filePath"))
{
    sw.Write(sb.ToString());
}

or

TextReader reader = new StreamReader(stream);
string line;
String newLines[];
int index = 0;
while ((line = reader.ReadLine()) != null)
{
   if (someCondition)
   {
      //Change variable line as you wish.
   }
   newLines[index] = line;
   index++;
}

using (StreamWriter sw = new StreamWriter("filePath"))
{
    foreach (string l in newLines)
    {
        sw.WriteLine(l);
    }
}

If memory is too important you can try this too:

TextReader reader = new StreamReader(stream);
string line;
while ((line = reader.ReadLine()) != null)
{
   if (someCondition)
   {
      //Change variable line as you wish.
   }
   using (StreamWriter sw = new StreamWriter("filePath"))
   {
       sw.WriteLine(line);
   }
 }