Question

In a Windows Forms C# app, I have a textbox where users paste log data, and it sorts it. I need to check each line individualy so I split the input by the new line, but if there are a lot of lines, greater than 100,000 or so, it throws a OutOfMemoryException.

My code looks like this:

StringSplitOptions splitOptions = new StringSplitOptions();
if(removeEmptyLines_CB.Checked)
    splitOptions = StringSplitOptions.RemoveEmptyEntries;
else
    splitOptions = StringSplitOptions.None;

List<string> outputLines = new List<string>();

foreach(string line in input_TB.Text.Split(new string[] { "\r\n", "\n" }, splitOptions))
{
    if(line.Contains(inputCompare_TB.Text))
        outputLines.Add(line);
}
output_TB.Text = string.Join(Environment.NewLine, outputLines);

The problem comes from when I split the textbox text by line, here input_TB.Text.Split(new string[] { "\r\n", "\n" }

Is there a better way to do this? I’ve thought about taking the first X amount of text, truncating at a new line and repeat until everything has been read, but this seems tedious. Or is there a way to allocate more memory for it?

Thanks,
Garrett

Update

Thanks to Attila, I came up with this and it seems to work. Thanks

StringReader reader = new StringReader(input_TB.Text);
string line;
while((line = reader.ReadLine()) != null)
{
    if(line.Contains(inputCompare_TB.Text))
        outputLines.Add(line);
}
output_TB.Text = string.Join(Environment.NewLine, outputLines);

Answer 1

The better way to do this would be to extract and process one line at a time, and use a StringBuilder to create the result:

StringBuilder outputTxt = new StringBuilder();
string txt = input_TB.Text;
int txtIndex = 0;
while (txtIndex < txt.Length) {
  int startLineIndex = txtIndex;
GetMore:
  while (txtIndex < txt.Length && txt[txtIndex] != '\r'  && txt[txtIndex] != '\n')) {
    txtIndex++;
  }
  if (txtIndex < txt.Length && txt[txtIndex] == '\r' && (txtIndex == txt.Length-1 || txt[txtIndex+1] != '\n') {
    txtIndex++;
    goto GetMore; 
  }
  string line = txt.Substring(startLineIndex, txtIndex-startLineIndex);
  if (line.Contains(inputCompare_TB.Text)) {
    if (outputTxt.Length > 0)
      outputTxt.Append(Environment.NewLine);
    outputTxt.Append(line); 
  }
  txtIndex++;
} 
output_TB.Text = outputTxt.ToString(); 

Pre-emptive comment: someone will object to the goto – but it is what’s needed here, the alternatives are much more complex (reg exp for example), or fake the goto with another loop and continue or break

Using a StringReader to split the lines is a much cleaner solution, but it does not handle both \r\n and \n as a new line:

StringReader reader = new StringReader(input_TB.Text); 
StringBuilder outputTxt = new StringBuilder();
string compareTxt = inputCompare_TB.Text;
string line; 
while((line = reader.ReadLine()) != null) { 
  if (line.Contains(compareTxt)) {
    if (outputTxt.Length > 0)
      outputTxt.Append(Environment.NewLine);
    outputTxt.Append(line); 
  }
} 
output_TB.Text = outputTxt.ToString();