We Keep Coding

How to overwrite text in same text file

I am in a fight with overwriting of a text file with some of changes using a console application. Here I am reading the file line by line. Can any one help me.
StreamReader sr = new StreamReader(#"C:\abc.txt");
string line;
line = sr.ReadLine();
while (line != null)
{
if (line.StartsWith("<"))
{
if (line.IndexOf('{') == 29)
{
string s = line;
int start = s.IndexOf("{");
int end = s.IndexOf("}");
string result = s.Substring(start+1, end - start - 1);
Guid g= Guid.NewGuid();
line = line.Replace(result, g.ToString());
File.WriteAllLines(#"C:\abc.txt", line );
}
}
Console.WriteLine(line);
line = sr.ReadLine();
}
//close the file
sr.Close();
Console.ReadLine();
Here I am getting the error file is already open by another process.
Please help me, anyone. Main task is to overwrite the same texfile with modifications

You need a single stream,
open it for both reading and writing.
FileStream fileStream = new FileStream(
#"c:\words.txt", FileMode.OpenOrCreate,
FileAccess.ReadWrite, FileShare.None);
now you can use fileStream.Read() and fileStream.Write() methods
please see this link for extended discussion
How to both read and write a file in C#

The problem is that you're trying to write to a file that is used by the StreamReader. You have to close it or - better - use the using-statement which disposes/closes it even on error.
using(StreamReader sr = new StreamReader(#"C:\abc.txt"))
{
// ...
}
File.WriteAllLines(...);
File.WriteAllLines also writes all lines to the file not only the currrent line, so it's pointless to do it in the loop.
Can i suggest you a different method to read the lines of a text-file? You can use File.ReadAllLines which reads all lines into a string[] or File.ReadLines which works similar to a StreamReader by reading all lines lazily.
Here's a version doing the same but using a ( more readable?) LINQ query:
var lines = File.ReadLines(#"C:\abc.txt")
.Where(l => l.StartsWith("<") && l.IndexOf('{') == 29)
.Select(l =>
{
int start = l.IndexOf("{");
int end = l.IndexOf("}", start);
string result = l.Substring(start + 1, end - start - 1);
Guid g = Guid.NewGuid();
return l.Replace(result, g.ToString());
}).ToList();
File.WriteAllLines(#"C:\abc.txt", lines);

Problem is that you have opened the file and reading from same file at the same time you are writing in that file. But what you should do is,
Read the changes from the file
Close the file
Write the contents back to file
So your code should be like
List<string> myAppendedList = new List<string>();
using (StreamReader sr = new StreamReader(#"C:\abc.txt"))
{
string line;
line = sr.ReadLine();
while (line != null)
{
if (line.StartsWith("<"))
{
if (line.IndexOf('{') == 29)
{
string s = line;
int start = s.IndexOf("{");
int end = s.IndexOf("}");
string result = s.Substring(start + 1, end - start - 1);
Guid g = Guid.NewGuid();
line = line.Replace(result, g.ToString());
myAppendedList.Add(line);
}
}
Console.WriteLine(line);
line = sr.ReadLine();
}
}
if(myAppendedList.Count > 0 )
File.WriteAllLines(#"C:\abc.txt", myAppendedList);

How to prevent adding an empty line to my file?

Im creating a text file and the last line is ""
private void lastRunDate()
{
String lastLine = readLastDate();
String[] date = lastLine.Split('/');
DateTime dt = new DateTime(Int32.Parse(date[2]), Int32.Parse(date[0]), Int32.Parse(date[1]));
DateTime currentDT = DateTime.Now;
argValue = 1;
if ((dt.Month == currentDT.Month) && (argValue == 0))
{
MessageBox.Show("This application has already been run this month");
this.Close();
}
}
private void AddRecordToFile()
{
DateTime now = DateTime.Now;
prepareToEmail();
string path = filepath;
bool dirtyData = true;
// This text is added only once to the file.
if (!File.Exists(path))
{
// Create a file to write to.
using (StreamWriter sw = File.CreateText(path))
{
sw.Write(now.ToShortDateString());
}
dirtyData = false;
}
if (dirtyData)
{
// This text is always added, making the file longer over time
// if it is not deleted.
using (StreamWriter sw = File.AppendText(path))
{
sw.Write(now.ToShortDateString());
}
}
}
private String readLastDate()
{
using (StreamReader sr = new StreamReader(filepath))
{
// Initialize to null so we are not stuck in loop forever in case there is nothing in the file to read
String line = null;
do
{
line = sr.ReadLine();
// Is this the end of the file?
if (line == null)
{
// Yes, so bail out of loop
return "01/01/1900"; // I had to put something
}
// Is the line empty?
if (line == String.Empty)
{
// Yes, so skip it
continue;
}
// Here you process the non-empty line
return line;
} while (true);
}
}
is what I am using to create the file (or append it)
now is a DateTime object
I used your (Karl) code to create a method called "readLastDate()"
I get the 1st date instead.

I'm probably being way to pragmatic and simple, but skip all the stream stuff and use File class directly like this...
string newLine = "";
if (!isFirstLine)
newLine = Environment.NewLine;
File.AppendAllText(
filePath,
string.Format("{0}{1}", newLine, DateTime.Now.ToString()));

You could use a sw.Write and PRE-pend a linefeed. Unfortunately that will give you an empty line at the start of the file.

Have you tried using the command .Trimend ('\n')?
http://msdn.microsoft.com/en-us/library/system.string.trimend.aspx

Do this:
sw.Write(now.ToShortDateString());
Here is the MSDN documentation for StreamWriter.WriteLine.
Here is the MSDN documentation for StreamWriter.Write.
UPDATE:
Keep using the WriteLine, but change the way you read your values in from the file:
using (StreamReader sr = new StreamReader(path))
{
// Initialize to null so we are not stuck in loop forever in case there is nothing in the file to read
String line = null;
do
{
line = sr.ReadLine();
// Is this the end of the file?
if (line == null)
{
// Yes, so bail out of loop
return;
}
// Is the line empty?
if (line == String.Empty)
{
// Yes, so skip it
continue;
}
// Here you process the non-empty line
} while (true);
}

Adding a record should be a simple matter of calling File.AppendAllText, as pointed out in another answer. Although I would recommend:
File.AppendAllText(filePath, DateTime.Now.ToString() + Environment.NewLine);
To read the last date from the file is also very easy:
string lastGoodLine = "01/01/1900";
using (StringReader sr = new StringReader(filePath))
{
while (!sr.EndOfStream)
{
string line = sr.ReadLine();
if (!string.IsNullOrEmpty(line))
lastGoodLine = line;
}
}
return lastGoodLine;

Reading the next line of a file only once

I have an application that reads information from a text file and then categorizes them and puts them onto a Database. For one category, I need to check the line that comes right after the current line and look for a certain keyword?
How do i get to read this line? This should happen when the streamreader has the current line already open....
I'm using c# on VS2010.
Edit:
All of the code below is in a while (!sReader.EndOfStream) loop
string line = sReader.ReadLine(); //Note: this is used way above and lots of things are done before we come to this loop
for (int i = 0; i < filter_length; i++)
{
if (searchpattern_queries[i].IsMatch(line) == true)
{
logmessagtype = selected_queries[i];
//*Here i need to add a if condition to check if the type is "RESTARTS" and i need to get the next line to do more classification. I need to get that line only to classify the current one. So, I'd want it to be open independently *
hit = 1;
if (logmessagtype == "AL-UNDEF")
{
string alid = AlarmID_Search(line);
string query = "SELECT Severity from Alarms WHERE ALID like '" +alid +"'";
OleDbCommand cmdo = new OleDbCommand(query, conn);
OleDbDataReader reader;
reader = cmdo.ExecuteReader();
while (reader.Read())
{
if (reader.GetString(0).ToString() == null)
{ }
else
{
string severity = reader.GetString(0).ToString();
if (severity == "1")
//Keeps going on.....
Also, the .log files that are opened might go upto 50 Mb types... ! Which is why i dont really prefer reading all lines and keeping track!

Here is an idiom to process the current line you while having the next line already available:
public void ProcessFile(string filename)
{
string line = null;
string nextLine = null;
using (StreamReader reader = new StreamReader(filename))
{
line = reader.ReadLine();
nextLine = reader.ReadLine();
while (line != null)
{
// Process line (possibly using nextLine).
line = nextLine;
nextLine = reader.ReadLine();
}
}
}
This is basically a queue with a maximum of two items in it, or "one line read-ahead".
Edit: Simplified.

Simply use
string[] lines = File.ReadAllLines(filename);
and process the file with a for (int i = 0; i < lines.Length; i ++) loop.
For a big file, simply cache the 'previous line' or do an out-of-band ReadLine().

Can you not just call reader.ReadLine() again? Or is the problem that you then need to use the line in the next iteration of the loop?
If it's a reasonably small file, have you considered reading the whole file using File.ReadAllLines()? That would probably make it simpler, although obviously a little less clean in other ways, and more memory-hungry for large files.
EDIT: Here's some code as an alternative:
using (TextReader reader = File.OpenText(filename))
{
string line = null; // Need to read to start with
while (true)
{
if (line == null)
{
line = reader.ReadLine();
// Check for end of file...
if (line == null)
{
break;
}
}
if (line.Contains("Magic category"))
{
string lastLine = line;
line = reader.ReadLine(); // Won't read again next iteration
}
else
{
// Process line as normal...
line = null; // Need to read again next time
}
}
}

You could save the position of the stream then after calling ReadLine, seek back to that position. However this is pretty inefficient.
I would store the result of ReadLine into a "buffer", and when possible use that buffer as a source. When it is empty, use ReadLine.

I am not really a file IO expert... but why not do something like this:
Before you start reading lines declare two variables.
string currentLine = string.Empty
string previousLine = string.Empty
Then while you are reading...
previousLine = currentLine;
currentLine = reader.ReadLine();

How to skip first line and start reading file from second line in C#

How to start reading file from 2nd line skipping 1st line. This seems to work but is it best way to do so?
using (StreamReader sr = new StreamReader(varFile, Encoding.GetEncoding(1250))) {
string[] stringSeparator = new string[] { "\",\"" };
int i = 0;
while (!sr.EndOfStream) {
string line = sr.ReadLine(); //.Trim('"');
if (i > 0) {
string[] values = line.Split(stringSeparator, StringSplitOptions.None);
for (int index = 0; index < values.Length; index++) {
MessageBox.Show(values[index].Trim('"'));
}
}
i++;
}
}

If the file is not very large and can fit in memory:
foreach (var line in File.ReadAllLines(varFile, Encoding.GetEncoding(1250)).Skip(1))
{
string[] values = line.Split(',');
...
}
If not write an iterator:
public IEnumerable<string> ReadAllLines(string filename, Encoding encoding)
{
using (var reader = new StreamReader(filename, encoding))
{
string line;
while ((line = reader.ReadLine()) != null)
{
yield return line;
}
}
}
and then consume it:
foreach (var line in ReadAllLines(varFile, Encoding.GetEncoding(1250)).Skip(1))
{
string[] values = line.Split(',');
...
}

Could you not just read the first line outside of the loop without assigning it to a variable?
using (StreamReader sr = new StreamReader(varFile, Encoding.GetEncoding(1250))) {
string[] stringSeparator = new string[] { "\",\"" };
if (!sr.EndOfStream)
sr.ReadLine();
while (!sr.EndOfStream) {
string line = sr.ReadLine(); //.Trim('"');
string[] values = line.Split(stringSeparator, StringSplitOptions.None);
for (int index = 0; index < values.Length; index++) {
MessageBox.Show(values[index].Trim('"'));
}
}
}

I'm sorry but I see no problem with the way you are doing it though. I couldn't add comment.
So just for the sake of answering, you probably could have try to call ReadLine() once before the loop. Might not be the best way as I don't know whats the behavior of running ReadLine() if its already end of stream, but it nothing is gonna happen then thats gonna save you some checks.
Updated:
To give a more complete answer, calling ReadLine() when the stream is at its end will return a null.
Reference: http://msdn.microsoft.com/en-us/library/system.io.streamreader.readline.aspx
Remember to check the return for null value.

Delete specific line from a text file?

I need to delete an exact line from a text file but I cannot for the life of me workout how to go about doing this.
Any suggestions or examples would be greatly appreciated?
Related Questions
Efficient way to delete a line from a text file (C#)

If the line you want to delete is based on the content of the line:
string line = null;
string line_to_delete = "the line i want to delete";
using (StreamReader reader = new StreamReader("C:\\input")) {
using (StreamWriter writer = new StreamWriter("C:\\output")) {
while ((line = reader.ReadLine()) != null) {
if (String.Compare(line, line_to_delete) == 0)
continue;
writer.WriteLine(line);
}
}
}
Or if it is based on line number:
string line = null;
int line_number = 0;
int line_to_delete = 12;
using (StreamReader reader = new StreamReader("C:\\input")) {
using (StreamWriter writer = new StreamWriter("C:\\output")) {
while ((line = reader.ReadLine()) != null) {
line_number++;
if (line_number == line_to_delete)
continue;
writer.WriteLine(line);
}
}
}

The best way to do this is to open the file in text mode, read each line with ReadLine(), and then write it to a new file with WriteLine(), skipping the one line you want to delete.
There is no generic delete-a-line-from-file function, as far as I know.

One way to do it if the file is not very big is to load all the lines into an array:
string[] lines = File.ReadAllLines("filename.txt");
string[] newLines = RemoveUnnecessaryLine(lines);
File.WriteAllLines("filename.txt", newLines);

Hope this simple and short code will help.
List linesList = File.ReadAllLines("myFile.txt").ToList();
linesList.RemoveAt(0);
File.WriteAllLines("myFile.txt"), linesList.ToArray());
OR use this
public void DeleteLinesFromFile(string strLineToDelete)
{
string strFilePath = "Provide the path of the text file";
string strSearchText = strLineToDelete;
string strOldText;
string n = "";
StreamReader sr = File.OpenText(strFilePath);
while ((strOldText = sr.ReadLine()) != null)
{
if (!strOldText.Contains(strSearchText))
{
n += strOldText + Environment.NewLine;
}
}
sr.Close();
File.WriteAllText(strFilePath, n);
}

You can actually use C# generics for this to make it real easy:
var file = new List<string>(System.IO.File.ReadAllLines("C:\\path"));
file.RemoveAt(12);
File.WriteAllLines("C:\\path", file.ToArray());

This can be done in three steps:
// 1. Read the content of the file
string[] readText = File.ReadAllLines(path);
// 2. Empty the file
File.WriteAllText(path, String.Empty);
// 3. Fill up again, but without the deleted line
using (StreamWriter writer = new StreamWriter(path))
{
foreach (string s in readText)
{
if (!s.Equals(lineToBeRemoved))
{
writer.WriteLine(s);
}
}
}

Read and remember each line
Identify the one you want to get rid
of
Forget that one
Write the rest back over the top of
the file

I cared about the file's original end line characters ("\n" or "\r\n") and wanted to maintain them in the output file (not overwrite them with what ever the current environment's char(s) are like the other answers appear to do). So I wrote my own method to read a line without removing the end line chars then used it in my DeleteLines method (I wanted the option to delete multiple lines, hence the use of a collection of line numbers to delete).
DeleteLines was implemented as a FileInfo extension and ReadLineKeepNewLineChars a StreamReader extension (but obviously you don't have to keep it that way).
public static class FileInfoExtensions
{
public static FileInfo DeleteLines(this FileInfo source, ICollection<int> lineNumbers, string targetFilePath)
{
var lineCount = 1;
using (var streamReader = new StreamReader(source.FullName))
{
using (var streamWriter = new StreamWriter(targetFilePath))
{
string line;
while ((line = streamReader.ReadLineKeepNewLineChars()) != null)
{
if (!lineNumbers.Contains(lineCount))
{
streamWriter.Write(line);
}
lineCount++;
}
}
}
return new FileInfo(targetFilePath);
}
}
public static class StreamReaderExtensions
{
private const char EndOfFile = '\uffff';
/// <summary>
/// Reads a line, similar to ReadLine method, but keeps any
/// new line characters (e.g. "\r\n" or "\n").
/// </summary>
public static string ReadLineKeepNewLineChars(this StreamReader source)
{
if (source == null)
throw new ArgumentNullException(nameof(source));
char ch = (char)source.Read();
if (ch == EndOfFile)
return null;
var sb = new StringBuilder();
while (ch != EndOfFile)
{
sb.Append(ch);
if (ch == '\n')
break;
ch = (char)source.Read();
}
return sb.ToString();
}
}

Are you on a Unix operating system?
You can do this with the "sed" stream editor. Read the man page for "sed"

What?
Use file open, seek position then stream erase line using null.
Gotch it? Simple,stream,no array that eat memory,fast.
This work on vb.. Example search line culture=id where culture are namevalue and id are value and we want to change it to culture=en
Fileopen(1, "text.ini")
dim line as string
dim currentpos as long
while true
line = lineinput(1)
dim namevalue() as string = split(line, "=")
if namevalue(0) = "line name value that i want to edit" then
currentpos = seek(1)
fileclose()
dim fs as filestream("test.ini", filemode.open)
dim sw as streamwriter(fs)
fs.seek(currentpos, seekorigin.begin)
sw.write(null)
sw.write(namevalue + "=" + newvalue)
sw.close()
fs.close()
exit while
end if
msgbox("org ternate jua bisa, no line found")
end while
that's all..use #d