Develop Reference

Input from any file in WPF Application is very Slow

I have a WPF Application which takes an input file path from user and then at the backend open the text file and try to read single character from the file.
fs = File.OpenRead(fileName);
var sr = new StreamReader(fs);
int c;
while ((c = sr.Read()) != -1)
{
Console.Write((char)c); //to check character read from file
try
{
frequencyMap.Add((char)c, 1);
}
catch
{
frequencyMap[(char)c] += 1;
}
}
Here frequencyMap is the dictionary in which character and it's frequency is stored.
This is one method no matter whatever i do the reading from file is always slow even if i try to read the whole text. On output window i see
Area selected is the part of input from the file.
Files upto 2KBs are fine but reading from files like 20KB really gives a hard time.
Now I read that using threads can solve this problem i just don't know how.
My Question is how can i read data from files fastly? if using threads is the solution then how to implement it?
i am new to this so kindly help me.
Thanks

Don't read it by character, read it for example by line, and process each string in a loop. Also Exception is not a way to check if the key exists in the Dictionary.
using (var sr = new StreamReader(fileName))
{
while (!sr.EndOfStream)
{
string s = sr.ReadLine();
Debug.WriteLine(s); //to check string read from file
foreach (char c in s)
{
if (frequencyMap.ContainsKey(c))
frequencyMap[c]++;
else
frequencyMap.Add(c, 1);
}
}
}

Firstly I hope the Console.WrieLine is purely test code. Writing to the console for every character will slow down your processing considerably.
Secondly, it appears from the screen shot you shared that your application is throwing a lot of exceptions. Throwing exceptions is not cheap either in a tight loop.
Thirdly I would recommend you profile your application (visual studio provides a profiler) to help you pin point where exactly your application is spending it’s time.

Best approach to replace specific lines in a text file in c#

For the following operation:
Open a text file
Search and replace all searching characters with new characters
I'd like to achieve above in c#, here is my code:
using (StreamReader sr = new StreamReader(#"S:\Personal Folders\A\TESTA.txt"))
{
using (StreamWriter sw = new StreamWriter(#"S:\Personal Folders\A\TESTB.txt"))
{
string line;
while ((line = sr.ReadLine())!= null)
{
if (!line.Contains("before"))
{
sw.WriteLine(line);
}
else if (line.Contains("before"))
{
sw.WriteLine(line.Replace("before", "after"));
}
}
}
}
Basically, the above code will generate a new file with the desired replace operation, but as you can see, the way I am doing is read each line of the original file and write to a new file. This could achieve my goal, but it may have system IO issue because it is reading and writing for each line. Also, I cannot read all the lines to an array first, and then write, because the file is large and if I try to write to an string[], replace all, then write the array to the file, will bring about the memory timeout issue.
Is there any way that I can just locate to the specific lines, and just replace those lines and keep all the rest? Or What is the best way to solve the above problem? Thanks

I don't know what IO issue you are worried about, but your code should work ok. You can code more concisely as follows:
using (StreamReader sr = new StreamReader(#"S:\Personal Folders\A\TESTA.txt"))
{
using (StreamWriter sw = new StreamWriter(#"S:\Personal Folders\A\TESTB.txt"))
{
while ((string line = sr.ReadLine())!= null)
{
sw.WriteLine(line.Replace("before", "after"));
}
}
}
This will run a bit faster because it searches for "before" only once per line. By default the StreamWriter buffers your writes and does not flush to the disk each time you call WriteLine, and file IO is asynchronous in the operating system, so don't worry so much about IO.

In general, what you are doing is correct, possibly followed by some renames to replace the original file. If you do want to replace the original file, you should rename the original file to a temporary name, rename the new file to the original name, and then either leave or delete the original file. You must handle conflicts with your temporary name and errors in all renames.
Consider you are replacing a six character string with a five character string - if you write back to the original file, what will you do with the extra characters? Files are stored on disk as raw bytes of data, there is no "text" file on disk. What if you replace a string with a longer one - you then potentially have to move the entire rest of the file to make room to write the longer line.
You can imagine the file on disk as letters written on graph paper in the boxes. The end of each line is noted by a special character (or characters - in Windows, that is CRLF), the characters fill all the boxes horizontally. If you tried to replace words on the graph paper you would have to erase and re-write lots of letters. Writing on a new sheet will be easiest.

Well, your approach is basically fine... but I wouldn't check if the line contains the word before... the trade-off is not good enough:
using (StreamReader sr = new StreamReader(#"S:\Personal Folders\A\TESTA.txt"))
{
using (StreamWriter sw = new StreamWriter(#"S:\Personal Folders\A\TESTB.txt"))
{
String line;
while ((line = sr.ReadLine()) != null)
sw.WriteLine(line.Replace("before", "after"));
}
}

Try following :
else if (line.Contains("before"))
{
sw.WriteLine(line.Replace("before", "after"));
sw.Write(sr.ReadToEnd());
break;
}

Get all lines after the last print of line with 'keyword' in C#

I am working on a c# project.
I am trying to send a logfile via email whenever application gets crashed.
however logfile is a little bit larger in size.
So I thought that i should include only a specific portion of logfile.
For that I am trying to read all the lines after the last instance of line with specified keyword.(in my case "Application Started")
since Application get restarted many times(due to crashing), 'Application Started' gets printed many times in file. So I would only want last print of line containing 'Application Started' & lines after that until end of file.
I require help to figure out how can i do this.
I have just started with Basic code as of now.
System.IO.StreamReader file = new System.IO.StreamReader("c:\\mylogfile.txt");
while((line = file.ReadLine()) != null)
{
if ( line.Contains("keyword") )
{
}
}

Read the file, line-by-line, until you find your keyword. Once you find your keyword, start pushing every line after that into a List<string>. If you find another line with your keyword, just Clear your list and start refilling it from that point.
Something like:
List<string> buffer = new List<string>();
using (var sin = new StreamReader("pathtomylogfile"))
{
string line;
bool read;
while ((line = sin.ReadLine())!=null)
{
if (line.Contains("keyword"))
{
buffer.Clear();
read = true;
}
if (read)
{
buffer.Add(line);
}
}
// now buffer has the last entry
// you could use string.Join to put it back together in a single string
var lastEntry = string.Join("\n",buffer);
}
If the number of lines in each entry is very large, it might be more efficient to scan the file first to find the last entry and then loop again to extract it. If the whole log file isn't that large, it might be more efficient to just ReadToEnd and then use LastIndexOf to find the start of the last entry.

Read everything from the file and then select the portion you want.
string lines = System.IO.File.ReadAllText("c:\\mylogfile.txt");
int start_index = lines.LastIndexOf("Application Started");
string needed_portion = lines.Substring(start_index);
SendEmail(needed_portion);

I advise you to use a proper logger, like log4net or NLogger.
You can configure it to save to multiple files - one containing complete logs, other containing errors/exceptions only. Also you can set maximum size of log files, etc. Or can configure them to send you a mail if exception occours.
Of course this does not solves your current problem, for it there is some solution above.
But I would try simpler methods, like trying out Notepad++ - it can handle bigger files (last time i've formatted a 30MB XML document with it, it took about 20 mins, but he did it! With simple text files there should be much better perf.). Or if you open the file for reading only (not for editing) you may get much better performance (in Windows).

Is it necessary to close a file after calling ReadAllText?

I am doing the following:
if (File.Exists(filePath))
{
string base64 = File.ReadAllText(filePath);
return new ImageContentDTO
{
ImageContentGuid = imageContentGuid,
Base64Data = base64
};
}
This works perfectly fine. What I want to ask is if I need to Close the file or anything similar after I am done reading from it. And if so, how?

No, you don't have to explicitly close the file, File.ReadAllText takes care of that for you.
The documentation contains this information very explicitly:
This method opens a file, reads each line of the file, and then adds each line as an element of a string. It then closes the file.
[...]
The file handle is guaranteed to be closed by this method, even if exceptions are raised.

You don't need to close anything when using File.ReadAllText since the underling stream reader is closed implicitely.
MSDN: File.ReadAllText
Opens a text file, reads all lines of the file, and then closes the
file.
Here's the implementation in .NET 4 (ILSpy):
string result;
using (StreamReader streamReader = new StreamReader(path, encoding))
{
result = streamReader.ReadToEnd();
}
return result;
The using statement disposes the StreamReader (even on error), that also closes it.

I know this question has been answered and this is almost a year now but for those who search and read this question, I would like to suggest you close a file when done with it, or at least do an investigation like my answer shows.
I am no programming expert but I have come across this situation recently.
I created a WinForms c# program and used File.ReadAllText to copy text to a string. Afterwards I tried to delete the file, directly from the folder not through the program, but I got an error that the file was still open in another program. I then stopped running the program and was able to delete the file.
That's my experience in Visual Studio 2012 Ultimate. It might be supposed to do something different, but that's what it did for me.
When I used StreamReader.ReadToEnd then StreamReader.Close on the same file, I had no problem deleting the file while running the program.

You have to close IDisposable instances only, usually by means of using, e.g.:
// StreamReader is IDisposable and should be Closed/Disposed
// either explicitly or by using
using (StreamReader sr = new StreamReader(filePath)) {
String base64 = sr.ReadToEnd();
...
}
since you don't have an IDisposable instance in your code (File.ReadAllText
returns String which is not IDisposable) you have nothing to Close/Dispose

StreamWriter outputFile = new StreamWriter(#"C:\Users\Marc\Desktop\_App\files\Data" + dat1 + ".txt");
outputFile.WriteLine(sb.ToString());
outputFile.Close();
StreamWriter outputFileex = new StreamWriter(#"C:\Users\Marc\Desktop\_App\files\DataEx" + dat1 + ".txt");
outputFileex.WriteLine(sbex.ToString());
outputFileex.Close();
Here's a working example I just did with a stringbuilder: "sb". If I remove one of those closes' the file gets generated but the file shows up blank with no data. I had to add in a close to get it to work properly.

WP7 Isolated Storage Text Document Read Line

Is there a way using Isolated storage ie a Text document, to grab the text on a certain line.
I would like to save variables to a text document on my settings page of my app. Then go back to the main page and read the variable saved on line 3. I already know how to save them. just not read certain lines.
Also is the text document created by my app going to still be there if i close and reopen the app?

Try this
using( TextReader reader = new StreamReader(
new IsolatedStorageFileStream( "myFile.txt", System.IO.FileMode.Open,
IsolatedStorageFile.GetUserStoreForApplication() ) ) {
string line = reader.ReadLine(); // first line, discard
line = reader.ReadLine(); // second line, discard
line = reader.ReadLine(); // third line, read the variable value
}
However, you might be better off using the IsolatedStorageSettings class to store settings (the link contains example usage). Another option is to put all your settings into a serializable class and use an XmlSerializer to save / read the settings. Both these approaches would not require parsing the file manually.