CSCI 3328 Object Oriented CSCI 3328 Object Oriented Programming in C# Programming in C#

Chapter 11: Files and StreamsChapter 11: Files and Streams

1

Xiang Lian

The University of Texas – Pan American

Edinburg, TX 78539

lianx@utpa.edu

Objectives

• In this chapter, you will– Learn how to create, read, write, and update files– Know how to use classes File and Directory to

obtain information about files and directories on your computer

– Learn how to use LINQ to search through directories

– Get familiar with sequential-access file processing– Know how to use classes FileStream,

StreamReader, StreamWriter, FileStream, and BinaryFormatter, as well as yield return

2

Introduction

• Variables and arrays only offer temporary storage of data– Data are lost when the program terminates

• In contrast, files are used for long-term storage place– Persistent data

– Data are stored on secondary storage devices

3

Data Hierarchy

• Bits

• Characters (ASCII or Unicode)

• Fields

• Records

• Files– Record key– Sequential file

• Databases4

Files and Streams

• File as a sequential stream of bytes

• Each file ends with an end-of-file marker

• Windows keeps track of total number of bytes in a file

• When a file is opened an object is created and a stream is associated with the object

• Each program automatically gets 3 objects, Console.Out, Console.In and Console.Error

5

Classes File and Directory

• Files are organized in directories

• Class Directory provides capabilities for manipulating directories

• Class File has static methods:– AppendText, Copy, Create, CreateText, Delete,

Exists, GetCreationTime, GetLastAccessTime, GetLastWriteTime, Move, Open, OpenRead, OpenText, OpenWrite

6

Directory Class Static Methods

• CreateDirectory• Delete• Exists• GetDirectories• GetFiles• GetCreationTime• GetLastAccessTime• GetLastWriteTime• Move

7

Create a File to Read/Write

• Pre-defined class library– using System.IO;

• StreamWriter (for text output)– StreamWriter outFile = new StreamWriter(fileName);

• StreamReader (for text input)– StreamReader inFile = null;try{ using (inFile = new StreamReader(fileName))

{ outputTextBox.AppendText(inFile.ReadToEnd());}} catch(IOException){

MessageBox.Show("Error reading from file", "File Error", MessageBoxButton.OK, MessageBoxIcon.Error);

}

8

Write to the File

• string fileName="test.txt";• File.Exists(fileName)

– true, if fileName exists

• outFile.WriteLine("text");• Other methods

– File.GetCreationTime(fileName);

– File.GetLastWriteTime(fileName);

– File.GetLastAccessTime(fileName);

9

Read From the File

• inFile.ReadLine("text");

10

Close the File

• outFile.Close();• inFile.Close();

11

Directory

• Directory.Exists(Name);– true, if directory Name exists

• string [] directoryList = Directory.GetDirectories(Name);– Obtain a list of files and directories

12

Searching Directories with LINQ

• string currentDirectory;• currentDirectory = Directory.GetCurrentDirectory();• string [] files = Directory.GetFiles(currentDirectory);• string [] directories=Directory.GetDirectories(currentDirectory);• var extensions = (from file in files select Path.GetExtension(file)).Distinct();foreach(var extension in extensions){ var extensionCount = (from file in files

where Path.GetExtension(file)==extension select file).Count();

}13

Dictionary Class

• A class Dictionary is a collection of key/value pairs– In namespace System.Collections.Generic– Dictionary <string, int> found = new Dictionary <string, int>();

• Key is of string data type, and value is of int data type

• Methods– found.ContainsKey(extension)

• true, if the directory contains a key for the extension

– found.Add(extension, extensionCount);– found[extension]

• Returns the value of the key "extension"

– found.Keys• A collection of keys

14

Example of Deleting Filesvar backupFiles = from file in files where Path.GetExtension(file)==".bak"

select file;foreach (var backup in backupFiles){ DialogResult result = MessageBox.Show("Found backup file " + Path.GetFileName(backup) + ". Delete?", "Delete Backup",

MessageBoxButtons.YesNo, MessageBoxIcon.Question); if (result == DialogResult.Yes) {

File.Delete(backup); // delete the file with name in "backup"found[".bak"]--; // decrement the counterif (found[".bak"] == 0)

found.Remove(".bak"); // remove the key from dictionary }}

15

Create a Sequential File

• In C# files, the concept of a "record" does not exist• Therefore, you have to create structured files by

yourself– Use text and special characters to separate fields in the

record

16

Example of Creating a Sequential File

public class Record{ public int Account {get; set;} public string FirstName {get; set;} public string LastName {get; set;} public decimal Balance {get; set;}

public Record() :this(0, string.Empty, string.Empty, 0M){} public RecordSerializable (int acc, string fName, string lName, decimal bal) {

Account = acc;FirstName = fName;LastName = lName;Balance = bal;

}}

17

Example of Creating a Sequential File (cont'd)

• FileStream output = new FileStream (fileName, FileMode.OpenOrCreate, FileAccess.Write);

• StreamWriter fileWriter = new StreamWriter(output);

• Record record = new Record();• fileWriter.WriteLine(record.Account + ","

+ record.FirstName + ","

+ record.LastName + ","

+ record.Balance);18

Reading Data From a Sequential-Access Text File

• FileStream input = new FileStream(fileName, FileMode.Open, FileAccess.Read);

• StreamReader fileReader = new StreamReader(input);

• string inputRecord = fileReader.ReadLine();• string[] inputFields;• if (inputRecord != null) {

inputFields = inputRecord.Split(',');Record record = new Record(Convert.ToInt32(inputFields[0]),

inputFields[1], inputFields[2], Convert.ToDecimal(inputFields[3]));

}

19

Class BinaryFormatter

• Class BinaryFormatter– Under namespace System.Runtime.Serialization.Formatters.Binary

– Serializable(outFile, object) method• Write a serializable object to the output file

• Serialization– In a class that is marked with [Serializable] attribute or that implements

interface Iserializable, you must ensure that every instance variable in a class is also serializable

– All simple-type variables, strings, and arrays (without containing references) are serializable

20

Example of RecordSerializable Class

public class RecordSerializable{ [Serializable] public int Account {get; set;} public string FirstName {get; set;} public string LastName {get; set;} public decimal Balance {get; set;}

public RecordSerializable() :this(0, string.Empty, string.Empty, 0M){} public RecordSerializable (int acc, string fName, string lName, decimal bal) {

Account = acc;FirstName = fName;LastName = lName;Balance = bal;

}} 21

Example of RecordSerializable Class (cont'd)

BinaryFormatter formatter = new BinaryFormatter();

FileStream output = new FileStream(fileName, FileMode.OpenOrCreate, FileAccess.Write);

try{

RecordSerializable record = new RecordSerializable();

formatter.Serialize(output, record);

}

catch (SerializationException)

{

// …

}

catch (FormatException)

{

// …

}

22

Reading and Deserializing Data From a Binary File

BinaryFormatter reader = new BinaryFormatter();FileStream input = new FileStream(fileName, FileMode.Open, FileAccess.Read);

try{

RecordSerializable record = (RecordSerializable) reader.Deserialize(input);

}

catch (SerializationException)

{

input.Close();

}

23

Select Files from Chooser

• Recall this topic in lecture slides of Chapter 8

24

Obtaining File Name From Chooser

OpenFileDialog fDialog = new OpenFileDialog();

if (fDialog.ShowDialog() == DialogResult.OK)

{

fileName = (fDialog.FileName.ToString());

MessageBox.Show(fileName);

}

25

Reading From a FileStreamReader ofile = new StreamReader(fileName);while (ofile.Peek()!=-1){ string oneline = ofile.ReadLine(); MessageBox.Show(oneline,"Reading From File.."); string[] items = oneline.Split(','); onePerson.fName = items[0]; onePerson.lName = items[1]; onePerson.GPA = Convert.ToSingle(items[3]); onePerson.Tele = items[2]; friendsList.Add(onePerson);}ofile.Close(); 26

Writing to the File

StreamWriter outfile = new StreamWriter(fileName);

foreach (Info person in friendsList)

outfile.WriteLine(person.fName+","+person.lName+","+person.Tele+","+Convert.ToString(person.GPA));

outfile.Close();

27

28