15 Text files
- 1. Text FilesText Files Reading andWritingText FilesReading andWritingText Files Svetlin NakovSvetlin Nakov Telerik CorporationTelerik Corporation www.telerik.comwww.telerik.com
- 2. Table of ContentsTable of Contents 1.1. What is Stream?What is Stream? Stream BasicsStream Basics 1.1. Reading Text FilesReading Text Files TheThe StreamReaderStreamReader ClassClass 1.1. Writing Text FilesWriting Text Files TheThe StreamStreamWritWriterer ClassClass 1.1. Handling I/O ExceptionsHandling I/O Exceptions
- 3. What Is Stream?What Is Stream? Streams Basic ConceptsStreams Basic Concepts
- 4. What is Stream?What is Stream? Stream is the natural way to transfer data inStream is the natural way to transfer data in the computer worldthe computer world To read or write a file, we open a streamTo read or write a file, we open a stream connected to the file and access the dataconnected to the file and access the data through the streamthrough the stream Input streamInput stream Output streamOutput stream
- 5. Streams BasicsStreams Basics Streams are used for reading and writing dataStreams are used for reading and writing data into and from devicesinto and from devices Streams areStreams are ordered sequences of bytesordered sequences of bytes Provide consecutive access to its elementsProvide consecutive access to its elements Different types of streams are available toDifferent types of streams are available to access different data sources:access different data sources: File access, network access, memory streamsFile access, network access, memory streams and othersand others Streams are open before using them andStreams are open before using them and closed after thatclosed after that
- 6. ReadingText FilesReadingText Files Using theUsing the StreamReaderStreamReader ClassClass
- 7. TheThe StreamReaderStreamReader ClassClass System.IO.StreamReaderSystem.IO.StreamReader The easiest way to read a text fileThe easiest way to read a text file Implements methods for reading text lines andImplements methods for reading text lines and sequences of characterssequences of characters Constructed by file name or other streamConstructed by file name or other stream Can specify the text encoding (for Cyrillic useCan specify the text encoding (for Cyrillic use windows-1251windows-1251)) Works likeWorks like Console.Read()Console.Read() // ReadLine()ReadLine() butbut over text filesover text files
- 8. StreamReaderStreamReader MethodsMethods new StreamReader(fileName)new StreamReader(fileName) Constructor for creating reader from given fileConstructor for creating reader from given file ReadLine()ReadLine() Reads a single text line from the streamReads a single text line from the stream ReturnsReturns nullnull when end-of-file is reachedwhen end-of-file is reached ReadToEnd()ReadToEnd() Reads all the text until the end of the streamReads all the text until the end of the stream Close()Close() Closes the stream readerCloses the stream reader
- 9. Reading a text file and printing its content toReading a text file and printing its content to the console:the console: Specifying the text encoding:Specifying the text encoding: Reading a Text FileReading a Text File StreamReader reader = new StreamReader("test.txt");StreamReader reader = new StreamReader("test.txt"); string fileContents = streamReader.ReadToEnd();string fileContents = streamReader.ReadToEnd(); Console.WriteLine(fileContents);Console.WriteLine(fileContents); streamReader.Close();streamReader.Close(); StreamReader reader = new StreamReader(StreamReader reader = new StreamReader( "cyr.txt", Encoding.GetEncoding(""cyr.txt", Encoding.GetEncoding("windows-1251windows-1251"));")); // Read the file contents here ...// Read the file contents here ... reader.Close();reader.Close();
- 10. UsingUsing StreamReaderStreamReader – Practices– Practices TheThe StreamReaderStreamReader instances should alwaysinstances should always be closed by calling thebe closed by calling the Close()Close() methodmethod Otherwise system resources can be lostOtherwise system resources can be lost In C# the preferable way to close streams andIn C# the preferable way to close streams and readers is by the "readers is by the "usingusing" construction" construction It automatically calls theIt automatically calls the Close()Close()afterafter thethe usingusing construction is completedconstruction is completed using (<stream object>)using (<stream object>) {{ // Use the stream here. It will be closed at the end// Use the stream here. It will be closed at the end }}
- 11. Reading a Text File – ExampleReading a Text File – Example Read and display a text file line by line:Read and display a text file line by line: StreamReader reader =StreamReader reader = new StreamReader("somefile.txt");new StreamReader("somefile.txt"); using (reader)using (reader) {{ int lineNumber = 0;int lineNumber = 0; string line = reader.ReadLine();string line = reader.ReadLine(); while (line != null)while (line != null) {{ lineNumber++;lineNumber++; Console.WriteLine("Line {0}: {1}",Console.WriteLine("Line {0}: {1}", lineNumber, line);lineNumber, line); line = reader.ReadLine();line = reader.ReadLine(); }} }}
- 12. ReadingText FilesReadingText Files Live DemoLive Demo
- 13. WritingText FilesWritingText Files Using theUsing the StreamStreamWriterWriter ClassClass
- 14. TheThe StreamWriterStreamWriter ClassClass System.IO.StreamWriterSystem.IO.StreamWriter Similar toSimilar to StringReaderStringReader, but instead of, but instead of reading, it provides writing functionalityreading, it provides writing functionality Constructed by file name or other streamConstructed by file name or other stream Can define encodingCan define encoding For Cyrillic use "For Cyrillic use "windows-1251windows-1251"" StreamWriter streamWriter = new StreamWriter("test.txt",StreamWriter streamWriter = new StreamWriter("test.txt", false, Encoding.GetEncoding("windows-1251"));false, Encoding.GetEncoding("windows-1251")); StreamWriter streamWriter = new StreamWriter("test.txt");StreamWriter streamWriter = new StreamWriter("test.txt");
- 15. StreamWriterStreamWriter MethodsMethods Write()Write() Writes string or other object to the streamWrites string or other object to the stream LikeLike Console.WriteConsole.Write()() WriteLineWriteLine()() LikeLike Console.WriteConsole.WriteLine()Line() AutoFlushAutoFlush Indicates whether to flush the internal bufferIndicates whether to flush the internal buffer after each writingafter each writing
- 16. Writing to a Text File –Writing to a Text File – ExampleExample Create text file named "Create text file named "numbers.txtnumbers.txt" and print" and print in it the numbers from 1 to 20 (one per line):in it the numbers from 1 to 20 (one per line): StreamWriter streamWriter =StreamWriter streamWriter = new StreamWriter("numbers.txt");new StreamWriter("numbers.txt"); using (streamWriter)using (streamWriter) {{ for (int number = 1; number <= 20; number++)for (int number = 1; number <= 20; number++) {{ streamWriter.WriteLine(number);streamWriter.WriteLine(number); }} }}
- 17. WritingText FilesWritingText Files Live DemoLive Demo
- 18. Handling I/O ExceptionsHandling I/O Exceptions IntroductionIntroduction
- 19. What is Exception?What is Exception? "An event that occurs during the execution of the"An event that occurs during the execution of the program that disrupts the normal flow ofprogram that disrupts the normal flow of instructions“ – definition by Googleinstructions“ – definition by Google Occurs when an operation can not be completedOccurs when an operation can not be completed Exceptions tell that something unusual wasExceptions tell that something unusual was happened, e. g. error or unexpected eventhappened, e. g. error or unexpected event I/O operations throw exceptions when operationI/O operations throw exceptions when operation cannot be performed (e.g. missing file)cannot be performed (e.g. missing file) When an exception is thrown, all operations after itWhen an exception is thrown, all operations after it are not processedare not processed
- 20. How to Handle Exceptions?How to Handle Exceptions? UsingUsing try{}try{},, catch{}catch{} andand finally{}finally{} blocks:blocks: trytry {{ // Some exception is thrown here// Some exception is thrown here }} catch (<exception type>)catch (<exception type>) {{ // Exception is handled here// Exception is handled here }} finallyfinally {{ // The code here is always executed, no// The code here is always executed, no // matter if an exception has occurred or not// matter if an exception has occurred or not }}
- 21. Catching ExceptionsCatching Exceptions Catch block specifies the type of exceptionsCatch block specifies the type of exceptions that is caughtthat is caught IfIf catchcatch doesn’t specify its type, it catches alldoesn’t specify its type, it catches all types of exceptionstypes of exceptions trytry {{ StreamReader reader = new StreamReader("somefile.txt");StreamReader reader = new StreamReader("somefile.txt"); Console.WriteLine("File successfully open.");Console.WriteLine("File successfully open."); }} catch (FileNotFoundException)catch (FileNotFoundException) {{ Console.Error.WriteLine("Can not find 'somefile.txt'.");Console.Error.WriteLine("Can not find 'somefile.txt'."); }}
- 22. Handling ExceptionsHandling Exceptions When Opening a FileWhen Opening a File trytry {{ StreamReader streamReader = new StreamReader(StreamReader streamReader = new StreamReader( "c:NotExistingFileName.txt");"c:NotExistingFileName.txt"); }} catch (System.NullReferenceException exc)catch (System.NullReferenceException exc) {{ Console.WriteLine(exc.Message);Console.WriteLine(exc.Message); }} catch (System.IO.FileNotFoundException exc)catch (System.IO.FileNotFoundException exc) {{ Console.WriteLine(Console.WriteLine( "File {0} is not found!", exc.FileName);"File {0} is not found!", exc.FileName); }} catchcatch {{ Console.WriteLine("Fatal error occurred.");Console.WriteLine("Fatal error occurred."); }}
- 23. Handling I/OHandling I/O ExceptionsExceptions Live DemoLive Demo
- 24. Reading andReading and WritingText FilesWritingText Files More ExamplesMore Examples
- 25. Counting WordCounting Word Occurrences – ExampleOccurrences – Example Counting the number of occurrences of theCounting the number of occurrences of the word "word "foundmefoundme" in a text file:" in a text file: StreamReader streamReader =StreamReader streamReader = new StreamReader(@"....somefile.txt");new StreamReader(@"....somefile.txt"); int count = 0;int count = 0; string text = streamReader.ReadToEnd();string text = streamReader.ReadToEnd(); int index = text.IndexOf("foundme", 0);int index = text.IndexOf("foundme", 0); while (index != -1)while (index != -1) {{ count++;count++; index = text.IndexOf("foundme", index + 1);index = text.IndexOf("foundme", index + 1); }} Console.WriteLine(count);Console.WriteLine(count); What isWhat is missing in thismissing in this code?code?
- 26. Counting Word OccurrencesCounting Word Occurrences Live DemoLive Demo
- 27. Reading Subtitles – ExampleReading Subtitles – Example .......... {2757}{2803} Allen, Bomb Squad, Special Services...{2757}{2803} Allen, Bomb Squad, Special Services... {2804}{2874} State Police and the FBI!{2804}{2874} State Police and the FBI! {2875}{2963} Lieutenant! I want you to go to St. John's{2875}{2963} Lieutenant! I want you to go to St. John's Emergency...Emergency... {2964}{3037} in case we got any walk-ins from the street.{2964}{3037} in case we got any walk-ins from the street. {3038}{3094} Kramer, get the city engineer!{3038}{3094} Kramer, get the city engineer! {3095}{3142} I gotta find out a damage report. It's very{3095}{3142} I gotta find out a damage report. It's very important.important. {3171}{3219} Who the hell would want to blow up a department{3171}{3219} Who the hell would want to blow up a department store?store? .......... We are given a standard movie subtitles file:We are given a standard movie subtitles file:
- 28. Fixing Subtitles – ExampleFixing Subtitles – Example Read subtitles file and fix it’s timing:Read subtitles file and fix it’s timing: static void Main()static void Main() {{ trytry {{ // Obtaining the Cyrillic encoding// Obtaining the Cyrillic encoding System.Text.Encoding encodingCyr =System.Text.Encoding encodingCyr = System.Text.Encoding.GetEncoding(1251);System.Text.Encoding.GetEncoding(1251); // Create reader with the Cyrillic encoding// Create reader with the Cyrillic encoding StreamReader streamReader =StreamReader streamReader = new StreamReader("source.sub", encodingCyr);new StreamReader("source.sub", encodingCyr); // Create writer with the Cyrillic encoding// Create writer with the Cyrillic encoding StreamWriter streamWriter =StreamWriter streamWriter = new StreamWriter("fixed.sub",new StreamWriter("fixed.sub", false, encodingCyr);false, encodingCyr); (example continues)(example continues)
- 29. Fixing Subtitles – ExampleFixing Subtitles – Example trytry {{ string line;string line; while (while ( (line = streamReader.ReadLine()) != null)(line = streamReader.ReadLine()) != null) {{ streamWriter.WriteLine(FixLine(line));streamWriter.WriteLine(FixLine(line)); }} }} finallyfinally {{ streamReader.Close();streamReader.Close(); streamWriter.Close();streamWriter.Close(); }} }} catch (System.Exception exc)catch (System.Exception exc) {{ Console.WriteLine(exc.Message);Console.WriteLine(exc.Message); }} }} FixLine(line)FixLine(line) perform fixes on theperform fixes on the time offsets:time offsets: multiplication or/andmultiplication or/and addition with constantaddition with constant
- 30. Fixing Movie SubtitlesFixing Movie Subtitles Live DemoLive Demo
- 31. SummarySummary Streams are the main I/O mechanismsStreams are the main I/O mechanisms in .NETin .NET TheThe StreamReaderStreamReader class andclass and ReadLine()ReadLine() method are used to read text filesmethod are used to read text files TheThe StreamWriterStreamWriter class andclass and WriteLine()WriteLine() method are used to write text filesmethod are used to write text files Exceptions are unusual events or errorExceptions are unusual events or error conditionsconditions Can be handled byCan be handled by try-catch-finallytry-catch-finally blocksblocks
- 33. ExercisesExercises 1.1. Write a program that reads a text file and prints onWrite a program that reads a text file and prints on the console its odd lines.the console its odd lines. 2.2. Write a program that concatenates two text filesWrite a program that concatenates two text files into another text file.into another text file. 3.3. Write a program that reads a text file and inserts lineWrite a program that reads a text file and inserts line numbers in front of each of its lines. The resultnumbers in front of each of its lines. The result should be written to another text file.should be written to another text file. 4.4. Write a program that compares two text files line byWrite a program that compares two text files line by line and prints the number of lines that are the sameline and prints the number of lines that are the same and the number of lines that are different. Assumeand the number of lines that are different. Assume the files have equal number of lines.the files have equal number of lines.
- 34. Exercises (2)Exercises (2) 5.5. Write a program that reads a text file containing aWrite a program that reads a text file containing a square matrix of numbers and finds in the matrix ansquare matrix of numbers and finds in the matrix an area of size 2 x 2 with a maximal sum of its elements.area of size 2 x 2 with a maximal sum of its elements. The first line in the input file contains the size ofThe first line in the input file contains the size of matrix N. Each of the next N lines contain Nmatrix N. Each of the next N lines contain N numbers separated by space. The output should be anumbers separated by space. The output should be a single number in a separate text file. Example:single number in a separate text file. Example: 44 2 3 3 42 3 3 4 0 2 3 40 2 3 4 1717 3 73 7 1 21 2 4 34 3 3 23 2
- 35. Exercises (3)Exercises (3) 6.6. Write a program that reads a text file containing aWrite a program that reads a text file containing a list of strings, sorts them and saves them to anotherlist of strings, sorts them and saves them to another text file. Example:text file. Example: IvanIvan GeorgeGeorge PeterPeter IvanIvan MariaMaria MariaMaria GeorgeGeorge PeterPeter 6.6. Write a program that replaces all occurrences of theWrite a program that replaces all occurrences of the substring "start" with the substring "finish" in a textsubstring "start" with the substring "finish" in a text file. Ensure it will work with large files (e.g. 100 MB).file. Ensure it will work with large files (e.g. 100 MB). 7.7. Modify the solution of the previous problem toModify the solution of the previous problem to replace only whole words (not substrings).replace only whole words (not substrings).
- 36. Exercises (4)Exercises (4) 9.9. Write a program that deletes from given text file allWrite a program that deletes from given text file all odd lines. The result should be in the same file.odd lines. The result should be in the same file. 10.10. Write a program that extracts from given XML fileWrite a program that extracts from given XML file all the text without the tags. Example:all the text without the tags. Example: 11.11. Write a program that deletes from a text file allWrite a program that deletes from a text file all words that start with the prefix "test". Wordswords that start with the prefix "test". Words contain only the symbols 0...9, a...z, A…Z, _.contain only the symbols 0...9, a...z, A…Z, _. <?xml version="1.0"><student><name>Pesho</name> <age>21</age><interests count="3"><interest> Games</instrest><interest>C#</instrest><interest> Java</instrest></interests></student>
- 37. Exercises (5)Exercises (5) 12.12. Write a program that removes from a text file allWrite a program that removes from a text file all words listed in given another text file. Handle allwords listed in given another text file. Handle all possible exceptions in your methods.possible exceptions in your methods. 13.13. Write a program that reads a list of words from a fileWrite a program that reads a list of words from a file words.txtwords.txt and finds how many times each of theand finds how many times each of the words is contained in another filewords is contained in another file test.txttest.txt. The. The result should be written in the fileresult should be written in the file result.txtresult.txt andand the words should be sorted by the number of theirthe words should be sorted by the number of their occurrences in descending order. Handle all possibleoccurrences in descending order. Handle all possible exceptions in your methods.exceptions in your methods.
Editor's Notes
- #26: The missing code is the &quot;using&quot; block. The file should be properly closed.