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c# how to end streamreader

I am doing a project Windows form for assignment in Uni, I want to search an already created text file to match a first name and last name then write some additional information if the name and last name exist. I have the code constructed and showing no errors, however when I run and attempt to add information I am being provided with an error which essentially says the next process (Streamreader writer can not access the file as it is already in use by another process) I assume this process is streamreader, I have tried to code it to stop reading to no avail. I am in my first 3 months learning coding and would appreciate some assistance if possible, I have put a snippet of my code below.
//check if there is a file with that name
if (File.Exists(sFile))
{
using (StreamReader sr = new StreamReader(sFile))
{
//while there is more data to read
while (sr.Peek() != -1)
{
//read first name and last name
sFirstName = sr.ReadLine();
sLastName = sr.ReadLine();
}
{
//does this name match?
if (sFirstName + sLastName == txtSearchName.Text)
sr.Close();
}
//Process write to file
using (StreamWriter sw = new StreamWriter(sFile, true))
{
sw.WriteLine("First Name:" + sFirstName);
sw.WriteLine("Last Name:" + sLastName);
sw.WriteLine("Gender:" + sGender);
}

You are using your writer inside the reader, using the same file.
A using disposes the object inside it, after the closing curly braces.
using(StreamReader reader = new StreamReader("foo")){
//... some stuff
using(Streamwriter writer = new StreamWriter("foo")){
}
}
Do it like so :
using(StreamReader reader = new StreamReader("foo")){
//... some stuff
}
using(Streamwriter writer = new StreamWriter("foo")){
}

As per my comment regarding the using statement.
Rearrange to the below. I've tested locally and it seems to work.
using (StreamReader sr = new StreamReader(sfile))
{
//while there is more data to read
while (sr.Peek() != -1)
{
//read first name and last name
sFirstName = sr.ReadLine();
sLastName = sr.ReadLine();
//does this name match?
if (sFirstName + sLastName == txtSearchName.Text)
break;
}
}
using (StreamWriter sw = new StreamWriter(sfile, true))
{
sw.WriteLine("First Name:" + sFirstName);
sw.WriteLine("Last Name:" + sLastName);
sw.WriteLine("Gender:" + sGender);
}
I've replaced the sr.Close with a break statement to exit out. Closing the reader causes the subsequent peek to error as it's closed.
Also, I've noticed that you are not setting gender? unless its set elsewhere.
hope that helps

You can use FileStream. It gives you many options to work with file:
var fileStream = new FileStream("FileName", FileMode.Open,
FileAccess.Write, FileShare.ReadWrite);
var fileStream = new FileStream("fileName", FileMode.Open,
FileAccess.ReadWrite, FileShare.ReadWrite);

I think this is what you want/need. You can't append to a file the way you are trying to do it. Instead you'll want to read your input file, and write a temp file as you are reading through. And, whenever your line matches your requirements, then you can write the line with your modifications.
string inputFile = "C:\\temp\\StreamWriterSample.txt";
string tempFile = "C:\\temp\\StreamWriterSampleTemp.txt";
using (StreamWriter sw = new StreamWriter(tempFile))//get a writer ready
{
using (StreamReader sr = new StreamReader(inputFile))//get a reader ready
{
string currentLine = string.Empty;
while ((currentLine = sr.ReadLine()) != null)
{
if (currentLine.Contains("Clients"))
{
sw.WriteLine(currentLine + " modified");
}
else
{
sw.WriteLine(currentLine);
}
}
}
}
//now lets crush the old file with the new file
File.Copy(tempFile, inputFile, true);

Why does FileStream sometimes ignore invisible characters?

I have two blocks of code that I've tried using for reading data out of a file-stream in C#. My overall goal here is to try and read each line of text into a list of strings, but they are all being read into a single string (when opened with read+write access together)...
I am noticing that the first block of code correctly reads in all of my carriage returns and line-feeds, and the other ignores them. I am not sure what is really going on here. I open up the streams in two different ways, but that shouldn't really matter right? Well, in any case here is the first block of code (that correctly reads-in my white-space characters):
StreamReader sr = null;
StreamWriter sw = null;
FileStream fs = null;
List<string> content = new List<string>();
List<string> actual = new List<string>();
string line = string.Empty;
// first, open up the file for reading
fs = File.OpenRead(path);
sr = new StreamReader(fs);
// read-in the entire file line-by-line
while(!string.IsNullOrEmpty((line = sr.ReadLine())))
{
content.Add(line);
}
sr.Close();
Now, here is the block of code that ignores all of the white-space characters (i.e. line-feed, carriage-return) and reads my entire file in one line.
StreamReader sr = null;
StreamWriter sw = null;
FileStream fs = null;
List<string> content = new List<string>();
List<string> actual = new List<string>();
string line = string.Empty;
// first, open up the file for reading/writing
fs = File.Open(path, FileMode.Open);
sr = new StreamReader(fs);
// read-in the entire file line-by-line
while(!string.IsNullOrEmpty((line = sr.ReadLine())))
{
content.Add(line);
}
sr.Close();
Why does Open cause all data to be read as a single line, and OpenRead works correctly (reads data as multiple lines)?
UPDATE 1
I have been asked to provide the text of the file that reproduces the problem. So here it is below (make sure that CR+LF is at the end of each line!! I am not sure if that will get pasted here!)
;$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
;$$$$$$$$$ $$$$$$$
;$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
;
;
;
UPDATE 2
An exact block of code that reproduces the problem (using the text above for the file). In this case I am actually seeing the problem WITHOUT trying Open and only using OpenRead.
StreamReader sr = null;
StreamWriter sw = null;
FileStream fs = null;
List<string> content = new List<string>();
List<string> actual = new List<string>();
string line = string.Empty;
try
{
// first, open up the file for reading/writing
fs = File.OpenRead(path);
sr = new StreamReader(fs);
// read-in the entire file line-by-line
while(!string.IsNullOrEmpty((line = sr.ReadLine())))
{
content.Add(line);
}
sr.Close();
// now, erase the contents of the file
File.WriteAllText(path, string.Empty);
// make sure that the contents of the file have been erased
fs = File.OpenRead(path);
sr = new StreamReader(fs);
if (!string.IsNullOrEmpty(line = sr.ReadLine()))
{
Trace.WriteLine("Failed: Could not erase the contents of the file.");
Assert.Fail();
}
else
{
Trace.WriteLine("Passed: Successfully erased the contents of the file.");
}
// now, attempt to over-write the contents of the file
fs.Close();
fs = File.OpenWrite(path);
sw = new StreamWriter(fs);
foreach(var l in content)
{
sw.Write(l);
}
// read back the over-written contents of the file
fs.Close();
fs = File.OpenRead(path);
sr = new StreamReader(fs);
while (!string.IsNullOrEmpty((line = sr.ReadLine())))
{
actual.Add(line);
}
// make sure the contents of the file are correct
if(content.SequenceEqual(actual))
{
Trace.WriteLine("Passed: The contents that were over-written are correct!");
}
else
{
Trace.WriteLine("Failed: The contents that were over-written are not correct!");
}
}
finally
{
// close out all the streams
fs.Close();
// finish-up with a message
Trace.WriteLine("Finished running the overwrite-file test.");
}

Your new file generated by
foreach(var l in content)
{
sw.Write(l);
}
does not contain end-of-line characters because end-of-line characters are not included in content.
As #DaveKidder points out in this thread over here, the spec for StreamReader.ReadLine specifically says that the resulting line does not include end of line.
When you do
while(!string.IsNullOrEmpty((line = sr.ReadLine())))
{
content.Add(line);
}
sr.Close();
You are losing end of line characters.

Unexpected output when reading and writing to a text file

I am a bit new to files in C# and am having a problem. When reading from a file and copying to another, the last chunk of text is not being written. Below is my code:
StringBuilder sb = new StringBuilder(8192);
string fileName = "C:...rest of path...inputFile.txt";
string outputFile = "C:...rest of path...outputFile.txt";
using (StreamReader reader = File.OpenText(fileName))
{
char[] buffer = new char[8192];
while ((reader.ReadBlock(buffer, 0, buffer.Length)) != 0)
{
foreach (char c in buffer)
{
//do some function on char c...
sb.Append(c);
}
using (StreamWriter writer = File.CreateText(outputFile))
{
writer.Write(sb.ToString());
}
}
}
My aim was to read and write to a textfile in a buffered manner. Something that in Java I would achieve in the following manner:
public void encrypt(File inputFile, File outputFile) throws IOException
{
BufferedReader infromfile = null;
BufferedWriter outtofile = null;
try
{
String key = getKeyfromFile(keyFile);
if (key != null)
{
infromfile = new BufferedReader(new FileReader(inputFile));
outtofile = new BufferedWriter(new FileWriter(outputFile));
char[] buffer = new char[8192];
while ((infromfile.read(buffer, 0, buffer.length)) != -1)
{
String temptext = String.valueOf(buffer);
//some changes to temptext are done
outtofile.write(temptext);
}
}
}
catch (FileNotFoundException exc)
{
} // and all other possible exceptions
}
Could you help me identify the source of my problem?
If you think that there is possibly a better approach to achieve buffered i/o with text files, I would truly appreciate your suggestion.

There are a couple of "gotchas":
c can't be changed (it's the foreach iteration variable), you'll need to copy it in order to process before writing
you have to keep track of your buffer's size, ReadBlock fills it with characters which would make your output dirty
Changing your code like this looks like it works:
//extracted from your code
foreach (char c in buffer)
{
if (c == (char)0) break; //GOTCHA #2: maybe you don't want NULL (ascii 0) characters in your output
char d = c; //GOTCHA #1: you can't change 'c'
// d = SomeProcessingHere();
sb.Append(d);
}

Try this:
string fileName = #"";
string outputfile = #"";
StreamReader reader = File.OpenText(fileName);
string texto = reader.ReadToEnd();
StreamWriter writer = new StreamWriter(outputfile);
writer.Write(texto);
writer.Flush();
writer.Close();

Does this work for you?
using (StreamReader reader = File.OpenText(fileName))
{
char[] buffer = new char[8192];
bool eof = false;
while (!eof)
{
int numBytes = (reader.ReadBlock(buffer, 0, buffer.Length));
if (numBytes>0)
{
using (StreamWriter writer = File.CreateText(outputFile))
{
writer.Write(buffer, 0, numBytes);
}
} else {
eof = true;
}
}
}
You still have to take care of character encoding though!

If you dont care about carraign returns, you could use File.ReadAllText
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. A line is defined as a sequence of characters followed by a carriage return ('\r'), a line feed ('\n'), or a carriage return immediately followed by a line feed. The resulting string does not contain the terminating carriage return and/or line feed.
StringBuilder sb = new StringBuilder(8192);
string fileName = "C:...rest of path...inputFile.txt";
string outputFile = "C:...rest of path...outputFile.txt";
// Open the file to read from.
string readText = File.ReadAllText(fileName );
foreach (char c in readText)
{
// do something to c
sb.Append(new_c);
}
// This text is added only once to the file, overwrite it if it exists
File.WriteAllText(outputFile, sb.ToString());

Unless I'm missing something, it appears that your issue is that you're overwriting the existing contents of your output file on each blockread iteration.
You call:
using (StreamWriter writer = File.CreateText(outputFile))
{
writer.Write(sb.ToString());
}
for every ReadBlock iteration. The output of the file would only be the last chunk of data that was read.
From MSDN documentation on File.CreateText:
If the file specified by path does not exist, it is created. If the
file does exist, its contents are overwritten.

Special Characters in StreamWriter

I am using streamwriter to write a string into stream. Now when I access the data from the stream, it adds "\0\0\0" characters to end of the content. I have to append the stream contents, so it creates problem as I am not able to remove these characters by trim() or remove() or replace() methods.
Below is the code I am using:
FOR WRITING :
using (MemoryMappedViewStream stream = mmf.CreateViewStream())
{
using (StreamWriter writer = new StreamWriter(stream, System.Text.Encoding.Unicode))
{
try
{
string[] files = System.IO.Directory.GetFiles(folderName, "*.*", System.IO.SearchOption.AllDirectories);
foreach (string str in files)
{
writer.WriteLine(str);
}
// writer.WriteLine(folderName);
}
catch (Exception ex)
{
Debug.WriteLine("Unable to write string. " + ex);
}
finally
{
mutex.ReleaseMutex();
mutex.WaitOne();
}
}
}
FOR READING :
StringBuilder sb = new StringBuilder();
string str = #"D:\Other Files\Test_Folder\New Text Document.txt";
using (var stream = mmf.CreateViewStream())
{
System.IO.StreamReader reader = new System.IO.StreamReader(stream);
sb.Append(reader.ReadToEnd());
sb.ToString().Trim('\0');
sb.Append("\n" + str);
}
How can I prevent this?
[UPDATES]
Writing
// Lock
bool mutexCreated;
Mutex mutex = new Mutex(true, fileName, out mutexCreated);
if (!mutexCreated)
mutex = new Mutex(true);
try
{
using (MemoryMappedViewStream stream = mmf.CreateViewStream())
{
using (BinaryWriter writer = new BinaryWriter(stream))
{
try
{
string[] files = System.IO.Directory.GetFiles(folderName, "*.*", System.IO.SearchOption.AllDirectories);
foreach (string str in files)
{
writer.Write(str);
}
writer.Flush();
}
catch (Exception ex)
{
Debug.WriteLine("Unable to write string. " + ex);
}
finally
{
mutex.ReleaseMutex();
mutex.WaitOne();
}
}
}
}
catch (Exception ex)
{
Debug.WriteLine("Unable to monitor memory file. " + ex);
}
Reading
StringBuilder sb = new StringBuilder();
string str = #"D:\Other Files\Test_Folder\New Text Document.txt";
try
{
using (var stream = mmf.CreateViewStream())
{
System.IO.BinaryReader reader = new System.IO.BinaryReader(stream);
sb.Append(reader.ReadString());
sb.Append("\n" + str);
}
using (var stream = mmf.CreateViewStream())
{
System.IO.BinaryWriter writer = new System.IO.BinaryWriter(stream);
writer.Write(sb.ToString());
}
using (var stream = mmf.CreateViewStream())
{
System.IO.BinaryReader reader = new System.IO.BinaryReader(stream);
Console.WriteLine(reader.ReadString());
}
}
catch (Exception ex)
{
Debug.WriteLine("Unable to monitor memory file. " + ex);
}

No '\0' are getting appended by StreamWriter. These are just the content of the memory-mapped file, stuff that was there before you started writing. The StreamReader needs an end-of-file indicator to know when the stop reading. There isn't any in an mmf beyond the size of the section. Like the 2nd argument you pass to MemoryMappedFile.CreateNew(string, long).
Or in other words, you created a mmf that's too large to fit the stream. Well, of course, you didn't have the time machine to guess how large to make it. You definitely need to do something about it, trimming the zeros isn't good enough. That goes wrong the second time you write a stream that's shorter. The reader will now still sees the bytes from the previous stream content and they won't be zero.
This is otherwise a common headache with mmfs, they are just chunks of memory and a stream is a very poor abstraction of that. One of the big reasons it took so long for mmfs to get supported by .NET, even though they are a very core OS feature. You need pointers to map a mmf and that's just not well supported in a managed language.
I don't see a good way to teach StreamReader new tricks in this case. Copying the bytes from the mmf into a MemoryStream would fix the problem but rather defeats the point of a mmf.
Consider using a pipe instead.

Your combination of a MMF and TextWriter/TextReader, especially ReadToEnd() is not a good match.
A textReader needs the EOF concept of the underlying file and a MMF just does not supply that in the same way. You will get your strings stuffed with \0\0... up to the capacity of the MMF.
As a possible fix:
collect the strings to write in a StringBuilder
use a BinaryWriter to write it as 1 string
read it back with a BinaryReader.
Another options is to use WriteLine/ReadLine and define some EOF marker (empty line or special string).
The BinaryWriter will prefix the string with a length-prefix so that the Reader knows when to stop.

Program Shutdown Messes Up StreamWriter

Im working on a little ATM program and I'm stuck on a StreamWritter problem.
On load, my program must use a StreamReader to read in 4 .txt files all located in my bin/debug. Then the user is asked to either Deposit or Withdraw money from the bank accounts located in the .txt files. Everything works fine for the StreamReader which loads all the bank accounts on program loading and for the StreamWriter to write the changes in the .txt files when I add/remove money.
My problem is when I close the program, the loading of the files works just fine but I can't write in the files anymore. My StreamWriter jumps straight to the Catch part and cannot be instantiated. How is that possible if it worked just fine on first use.
Heres the StreamReader Code :
public bool ReadSavingAccount()
{
string strLine;
string[] strArray;
char[] charArray = new char[] { ',' };
FileStream aFile;
StreamReader sr;
try
{
aFile = new FileStream("mySavingAccount.txt", FileMode.Open);
sr = new StreamReader(aFile);
strLine = sr.ReadLine();
while (strLine != null)
{
strArray = strLine.Split(charArray);
Savings monSave = new Savings(strArray[0], Convert.ToDouble(strArray[1]));
mySavingAccount.Add(monSave);
strLine = sr.ReadLine();
}
sr.Close();
aFile.Close();
}
catch
{
return false;
}
return true;
}
And the StreamWrite Code:
public bool WriteSavingAccount()
{
FileStream aFile;
StreamWriter sw;
string myString;
try
{
aFile = new FileStream("mySavingAccount.txt", FileMode.Create);
sw = new StreamWriter(aFile);
}
catch
{
return false;
}
foreach (Savings mySave in mySavingAccount)
{
myString = mySave.AccountNumber + "," + mySave.AccountBalance;
sw.WriteLine(myString);
}
sw.Close();
return true;
}
Any idea what the problem could be ?
Thanks in advance and let me know if you need any other parts of the code.

Try adding a second parameter of boolean to your StreamWriter call. This is the append parameter. True to append to the file, false to overwrite it.
sw = new StreamWriter(aFile, false);

Create your StreamWriter in a using statement to ensure it is closed properly.