C# Files and Data Hierarchy

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Questions and Answers

What are files used for in computing?

Long-term retention of data (correct)

Short-term data storage

Real-time processing

Temporary data storage

C# uses the Unicode character set, where characters are composed of 8 bytes.

False

What is a field in the context of data hierarchy?

A group of characters that conveys meaning

A record is a collection of related __________ that contain data about an entity.

fields Signup and view all the answers

Match the following stream types with their description:

Base Streams = Read and write data from and to an external data storage mechanism Pass-through Streams = Read from and write to other streams, adding additional functionality like buffering and encoding Signup and view all the answers

Which class is used to write binary data to a file in C#?

BinaryWriter Signup and view all the answers

In C#, you cannot view the contents of a binary file using Notepad.

True Signup and view all the answers

The constructor for the FileStream object includes values for two enumerated types: FileMode.Open and FileAccess._.

Read Signup and view all the answers

Match the methods in the BinaryReader class with their descriptions:

Close() = Closes the current BinaryReader and the underlying stream PeekChar() = Returns the next available character and does not advance the byte or character position Read() = Reads characters from the underlying stream and advances the current position of the stream ReadBoolean() = Reads a Boolean value from the current stream and advances the current position of the stream by 1 byte Signup and view all the answers

Which class provides static methods for creating, copying, deleting, moving, and opening files, and aids in the creation of FileStream objects?

File Signup and view all the answers

What is the purpose of the StreamWriter class?

Implements a TextWriter for writing characters to a stream Signup and view all the answers

Enclose attempts to access text files inside ______ blocks.

try...catch Signup and view all the answers

The StreamWriter class has a method called AutoClose to close the stream.

False Signup and view all the answers

Match the StreamWriter method with its description:

Close() = Closes the current StreamWriter Dispose() = Releases the unmanaged resources used by the StreamWriter Flush() = Clears all buffers for the current writer and causes any buffered data to be written to the underlying stream Signup and view all the answers

To invoke a method in C#, the method name is preceded by the _______ name.

class Signup and view all the answers

What additional functionality do DirectoryInfo and FileInfo classes provide beyond File and Directory classes?

Both have public properties and public constructors. Neither can be inherited. Signup and view all the answers

What are some of the key properties of DirectoryInfo class?

Root Signup and view all the answers

Serialization is the process of converting objects into streams of bytes.

True Signup and view all the answers

What purpose does the BinaryFormatter class serve in C#?

The BinaryFormatter class enables entire objects to be written to or read from a stream. Signup and view all the answers

Match the FileInfo properties with their descriptions:

Attributes = Gets or sets the FileAttributes of the current FileSystemInfo. DirectoryName = Gets a string representing the directory's full path. Extension = Gets the string representing the extension part of the file. Name = Gets the name of the file. Signup and view all the answers

Study Notes

Introduction to Files in C#

Files are used for long-term retention of large amounts of data, even after the program terminates.
Data maintained in files is called persistent data.
Files are stored on secondary storage devices such as magnetic disks, optical disks, flash memory, and magnetic tapes.

Data Hierarchy

A bit is the smallest data item that computers support.
Bytes are composed of eight bits.
C# uses the Unicode character set, where characters are composed of 2 bytes.
A field is a group of characters that conveys meaning.
Records are collections of related fields that contain data about an entity.
Files are a group of related records.

File Types

Sequential Access Files: Each record is read in order based on its relative position.
Random Access Files: Records are not in any sequence and can be accessed in any order.

Files and Streams

C# views each file as a sequential stream of bytes.
Each file ends either with an end-of-file marker or at a specific byte number that is recorded in a system-maintained administrative data structure.

Understanding Streams

A stream functions as a pipeline or channel between an input device and an application, and potentially an output device.
Streams can be read from and written to other streams, adding additional functionality (e.g., buffering, encoding, and compression).

Types of Streams in .NET Framework

Base Streams: Read and write data from and to an external data storage mechanism.
Pass-through Streams: Read from and write to other streams, adding additional functionality (e.g., buffering, encoding, and compression).

Main Operations with Streams

Construct (Create): Connects to the data transfer/storage mechanism or to another stream.
Reading: Retrieves data from the stream.
Writing: Sends data to the stream.
Positioning: Moves the current stream position (if positioning is supported).
Closure: Completes the work on the stream and releases the used resources.

System.IO Classes

BinaryReader: Reads primitive data types as binary values.
BinaryWriter: Writes primitive types in binary to a stream.
Directory: Exposes static methods for creating and moving through directories and subdirectories.
DirectoryInfo: Exposes instance methods for creating and moving through directories and subdirectories.

Readers and Writers

TextReader: Represents a reader that can read a sequential series of characters.
TextWriter: Represents a writer that can write a sequential series of characters.
StreamReader: Reads text data from a stream.
StreamWriter: Writes text data to a stream.

File Streams

File Streams are used to read and write data to and from files.
StreamReader and StreamWriter classes are used to read and write text data to and from files.

Writing Text Files

Use the StreamWriter class to write text data to a file.
Use the Close() method to finish storing values.

StreamReader and StreamWriter Members

StreamReader Members: Close(), DiscardBufferedData(), Dispose(), Peek(), Read(), ReadBlock(), ReadLine(), ReadToEnd().
StreamWriter Members: AutoFlush (Property), Close(), Dispose(), Flush(), NewLine (Property), Write(), WriteLine().### File Streams
The FileStream class is used to work with file streams, inherits from the Stream class, and supports all its methods and properties.
It supports reading, writing, positioning (if the device where the file is located supports these operations).
In its constructor, it is set: file name, way to open the file, access mode, and access for competing users.

Constructing a File Stream

FileStream constructor: FileStream fs = new FileStream(string fileName, FileMode [, FileAccess [, FileShare]]);
FileMode: file opening mode (Open, Append, Create, CreateNew, OpenOrCreate, Truncate)
FileAccess: file access mode (Read, Write, ReadWrite)
FileShare: access mode for other users while we keep the file open (None, Read, Write, ReadWrite)

BinaryReader and BinaryWriter Classes

Used for writing and reading binary data, rather than character strings.
Files created are readable by the computer but cannot be opened and read using Notepad.
A program is needed to interpret the file contents.

BinaryWriter Class

Instantiates objects of the FileStream and BinaryWriter classes.
FileStream object is then sent as an argument to the BinaryWriter constructor.

BinaryReader Class

Cannot simply open a binary file in Notepad and view its contents.
Need to write program statements that use the BinaryReader class to retrieve the results.
Constructor for the FileStream object includes values for two enumerated types: FileMode.Open and FileAccess.Read.

File and Directory Classes

File class: contains methods to access information about files, contained in the System.IO namespace.
Directory class: provides information about directories or folders.

File and FileInfo Classes

Provide functionality to: Create file, Open a file, Copy file, Move (rename) a file, Delete file, Extract the time of last access and modification, Existence check.
The File class provides these methods statically and FileInfo by instance.

Directory and DirectoryInfo Classes

Provide functionality to: Create directories and subdirectories, Retrieve all files, Retrieve all subdirectories, Move (rename), Delete, Extract the parent directory, Existence check, Extract the full name.
The Directory class provides these methods statically and DirectoryInfo by instance.

File Class Static Members and Their Descriptions

AppendAllText(): Appends the specified string to the file, creating the file if it does not already exist.
AppendText(): Creates a StreamWriter that appends UTF-8 encoded text to an existing file or creates a file if one does not exist.
Copy(): Copies an existing file to a new file.
Create(): Creates a file in the specified path and returns its associated StreamWriter.
Delete(): Deletes the specified file.
Exists(): Determines whether the specified file exists.

Directory Class Public Static Members and Their Descriptions

CreateDirectory(): Creates all the directories in a specified path.
Delete(): Deletes a specified directory.
Exists(): Determines whether the given path refers to an existing directory.
GetCreationTime(): Gets the creation date and time of a directory.
GetCurrentDirectory(): Gets the current working directory of the application.

Utility Classes

Utility classes allow you to manipulate files and directory structures.
Aid in copying, moving, renaming, creating, opening, deleting, and appending files.
Expose only static members.
Objects are not instantiated from these classes.
To invoke the method, the method name is preceded by the class name (as opposed to an object’s name).### Environment Special Folders
Environment.GetFolderPath method is used to retrieve the path of special folders.
Some special folders include DesktopDirectory, MyDocuments, Favorites, and MyMusic.
The method returns a string representing the path of the specified special folder.

Understanding Serialization and Deserialization

Serialization is the process of converting objects into streams of bytes.
Deserialization is the process of converting streams of bytes back into objects.
Disadvantages of writing to a text file include:
- Data is easily readable and not secure.
- Converting each field to text and combining fields with delimiters is cumbersome.

Object Serialization in C#

Object serialization allows entire objects to be written to or read from a file.
A serialized object is an object represented as a sequence of bytes that includes the object's data, its type, and the types of data stored in the object.

BinaryFormatter Class

The BinaryFormatter class enables entire objects to be written to or read from a stream.
The Serialize method writes an object's representation to a file.
The Deserialize method reads the representation from a file and reconstructs the original object.
Both methods throw a SerializationException if an error occurs during serialization or deserialization.

Example Serializable Class

A class must be marked with the [Serializable] attribute to be serializable.
In a serializable class, every instance variable must also be serializable.
Example of a serializable class:
- [Serializable] class Employee with properties EmpNum, Name, and Salary.

Serializable Class Requirements

In a serializable class, every instance variable must also be serializable.
By default, all C# simple data types are serializable, including strings.
If a class contains fields that are more complex data types, they must be checked to ensure they are serializable.
Namespaces required for serialization:
- System.Runtime.Serialization.Formatters.Binary
- System.Runtime.Serialization

Serialization Example

Example of serializing an Employee object to a file and deserializing it back.
Using FileStream to create and read from a file.
Using BinaryFormatter to serialize and deserialize the object.

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Description

Learn about files in C# programming, including data hierarchy and storage. Understand bits, bytes, and Unicode character set in C#.