Unexpected output when reading and writing to a text file

Question

I'm a little new to C # files and I have a problem. When reading from a file and copying to another, the last piece of text is not 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 goal was to read and write to a text file in a buffered manner. What in Java I would achieve as follows:

 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 there is a better approach to getting buffered I / O with text files, I would appreciate your suggestion.

Answer 1

There are a couple of "gotchas":

• c cannot be changed (this is a foreach iteration variable), you will need to copy it to process before writing
• you need to track the size of your buffer, ReadBlock fills it with characters that could make your file dirty

Changing your code like this looks like this:

 //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); } 

Answer 2

Try the following:

  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(); 

Answer 3

If you don't care about carraign return, you can use File.ReadAllText

This method opens the file, reads each line of the file, and then adds each line as a line item. Then it 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 followed by a line. The received line does not contain the final carriage return and / or line.

 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()); 

Answer 4

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!

Answer 5

If something is missing for me, it seems that your problem is that you are overwriting the existing contents of your output file at each iteration of the blockread.

You call:

  using (StreamWriter writer = File.CreateText(outputFile)) { writer.Write(sb.ToString()); } 

for each iteration of ReadBlock. The output file will be only the last piece of data that has been read.

From the MSDN documentation for File.CreateText:

If the file specified by the path does not exist, it is created. If the file exists, its contents are overwritten.