Files in C# Programming
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Questions and Answers

Which class provides static methods for creating, copying, deleting, moving, and opening files?

  • FileStream
  • File (correct)
  • BinaryReader
  • StreamWriter

    • StreamWriter is used for reading characters from a byte stream.

    False

    What is the smallest data item that computers support?

    bit

    What is a group of related fields that contain data about an entity called?

    <p>Record</p> Signup and view all the answers

    What method is used to close the current StreamWriter?

    <p>Close()</p> Signup and view all the answers

    Each record in a sequential access file is read based on its relative position.

    <p>True</p> Signup and view all the answers

    The exception that is thrown when a file that does not exist on disk is accessed is ____________.

    <p>FileNotFoundException</p> Signup and view all the answers

    Match the StreamReader and StreamWriter members with their descriptions:

    <p>Close() = Closes the current StreamWriter ReadLine() = Reads a line of characters from the current stream and returns the data as a string WriteLine() = Writes the characters to the stream, followed by a line terminator</p> Signup and view all the answers

    C# considers characters to be composed of __ bytes in the Unicode character set.

    <p>2</p> Signup and view all the answers

    Match the following stream types with their descriptions:

    <p>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, encoding, and compression.</p> Signup and view all the answers

    What class provides functionality for working with paths in C#?

    <p>System.IO.Path</p> Signup and view all the answers

    What does the DirectoryInfo object returned by method CreateDirectory contain information about?

    <p>Parent and root directory</p> Signup and view all the answers

    Serialization is the process of converting objects into streams of bytes in C#.

    <p>True</p> Signup and view all the answers

    The ________ class enables entire objects to be written to or read from a stream.

    <p>BinaryFormatter</p> Signup and view all the answers

    Which classes are used for handling binary files in C#?

    <p>FileStream and BinaryWriter</p> Signup and view all the answers

    Can binary files be opened and read directly using Notepad?

    <p>False</p> Signup and view all the answers

    What is the purpose of the BinaryReader class in C#?

    <p>to read binary data from files</p> Signup and view all the answers

    Match the following file handling classes with their functionalities:

    <p>BinaryWriter = Writing binary data to files File = Accessing information about files Directory = Manipulating directories and folders BinaryReader = Reading binary data from files</p> Signup and view all the answers

    The Static Member __________ in the File class appends the specified string to the file.

    <p>AppendAllText()</p> Signup and view all the answers

    Study Notes

    Files in C#

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

    Data Hierarchy

    • The smallest data item that computers support is called a bit (short for “binary digit”—a digit that can assume one of two values).
    • Digits, letters, and special symbols are referred to as characters.
    • Bytes are composed of eight bits.
    • C# uses the Unicode character set (http://www.unicode.org) in which characters are composed of 2 bytes.
    • Just as characters are composed of bits, fields are composed of characters.
    • A field is a group of characters that conveys meaning.
    • Data items processed by computers form a data hierarchy, in which data items become larger and more complex in structure.

    Data Hierarchy (Continued)

    • A record is a collection of related fields that contain data about an entity.
    • A file is a group of related records.
    • To facilitate the retrieval of specific records from a file, at least one field in each record is chosen as a record key, which uniquely identifies a record.
    • A common file organization is called a sequential file, in which records typically are stored in order by a record-key field.
    • A group of related files often are stored in a database.
    • A collection of programs designed to create and manage databases is called a database management system (DBMS).

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

    Random Access File

    • Records are not in any sequence and can be accessed in any order.
    • A C# application opens a file by creating an object and associating a stream of bytes with that object.
    • When you finish using a file, the program should close the file.
    • Not closing a file may make it inaccessible.
    • Not closing an output file can result in data not being written to the file.

    Files and the File and Directory Classes

    • Folder or Directory: A location inside the root directory designed to group items or files that are similar in nature.
    • Path: A combination of the disk drive plus the complete hierarchy of directories in which a file resides.
    • Example: C:\C#\Chapter.07\Data.txt
    • C# provides built-in classes named File and Directory.
    • Contain methods to help you manipulate files and their directories.
    • Access information about files.
    • Create, delete, or move files.

    Enumerations

    • Enumeration - special form of value type that supplies alternate names for the values of an underlying primitive type.
    • Enumeration type has a name and a set of fields.
    • Example: public enum DayOfWeek { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday }
    • GetAttributes() returns an enumeration.
    • Enumerated values for FileAttributes include Archive, Compressed, Device, Directory, Encrypted, Hidden, Normal, ReadOnly, and System.
    • Using enumerations makes coding simpler and the output more readable.

    Streams

    • Stream: Functions as a pipeline or channel between an input device and an application, and potentially an output device.
    • 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).
    • Examples: FileStream, MemoryStream, NetworkStream, BufferedStream, CryptoStream.

    Main Operations with Streams

    • Construct (Create): The stream connects to the data transfer/storage mechanism or to another stream.
    • Reading: Data is retrieved from the stream.
    • Writing: Data is sent to the stream.
    • Positioning: Moves the current stream position (if positioning is supported).
    • Closure: The work on the stream is completed and the used resources are released.

    Base Class for Streams

    • The base class for all streams is the System.IO.Stream abstract class.
    • It defines methods for performing basic operations.
    • Not all streams support read, write, and position operations.
    • Which operations are supported can be checked using the CanRead, CanWrite, and CanSeek properties.
    • Streams that allow positioning support Position and Length properties.
    • There is a special Stream.Null stream that ignores all read and write attempts.

    Files and Streams (Continued)

    • When a console application executes, the runtime environment creates the Console.Out, Console.In, and Console.Error streams.
    • Console.In refers to the standard input stream object, which enables a program to input data from the keyboard.
    • Console.Out refers to the standard output stream object, which enables a program to output data to the screen.
    • Console.Error refers to the standard error stream object, which enables a program to output error messages to the screen.

    Files and Streams (Continued)

    • The System.IO namespace includes stream classes such as StreamReader, StreamWriter, and FileStream for file input and output.
    • These stream classes inherit from abstract classes TextReader, TextWriter, and Stream, respectively.
    • Abstract class Stream provides functionality for representing streams as bytes.
    • Classes FileStream, MemoryStream, and BufferedStream (all from namespace System.IO) inherit from class Stream.

    Files and Streams (Continued)

    • Class FileStream can be used to write data to and read data from files.
    • FileStream is used alone for bytes and with either StreamReader and StreamWriter for text, for either input from and output to a file.
    • StreamWriter class for writing data to text file.
    • Includes implementations for Write() and WriteLine().
    • StreamReader class to read or write to or from text files.
    • Includes implementations of Read() and ReadLine().

    System.IO Classes

    • Class Description
    • 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
    • DirectoryNotFoundException The exception that is thrown when part of a file or directory cannot be found
    • EndOfStreamException The exception that is thrown when reading is attempted past the end of a stream

    System.IO Classes (Continued)

    • Class Description
    • File Provides static methods for creating, copying, deleting, moving, and opening files, and aids in the creation of FileStream objects
    • FileInfo Provides instance methods for creating, copying, deleting, moving, and opening files, and aids in the creation of FileStream objects
    • FileLoadException The exception that is thrown when a file is found but cannot be loaded
    • FileNotFoundException The exception that is thrown when an attempt to access a file that does not exist on disk fails
    • FileStream Exposes a stream around a file, supporting both synchronous and asynchronous read and write operations

    Readers and Writers

    • Classes that make it easier to work with streams.
    • Allow reading and writing various data structures, such as primitive types, text information, and other types.
    • Can be binary or text.
    • TextReader and TextWriter Classes:
      • Abstract classes not used directly.
      • StreamReader - reads text data from a stream.
      • StringReader - reads text data from a string.
      • StreamWriter – writes text data to a stream.
      • StringWriter - writes text data to a string, uses StringBuilder internally.
    • BinaryReader and BinaryWriter Classes:
      • Provide reading and writing of primitive data types in binary form.
      • Methods: ReadChar(), ReadChars(), ReadInt32(), ReadDouble(),...
      • Methods: Write(char), Write(char[]), Write(Int32), Write(Double),...
      • Allow reading and writing a string by writing it as an array of characters preceded by its length: ReadString(), Write(string)

    File Streams (Continued)

    • System.IO namespace must be imported for files: using System.IO;
    • The bin\Debug or bin\Release subdirectory of the current project is used for file when you don’t specify a path.
    • Use verbatim string character (@) or escape sequence (\) to specify path:
      • @"C:\CSharpProjects\Proj1" or "c:\CSharpProjects\Proj1"

    File Streams (Continued)

    • Several abstract classes for dealing with files:
      • Stream, TextWriter, and TextReader
    • Stream classes provide generic methods for dealing with input/output
    • IO.Stream class and its subclasses – byte-level data
    • IO.TextWriter and IO.TextReader – data in a text (readable) format
    • StreamReader and StreamWriter derived classes of IO.TextWriter and IO.TextReader

    File Streams (Continued)

    • StreamWriter outputFile = new StreamWriter("someOutputFileName");
    • StreamReader inputFile = new StreamReader("someInputFileName");
    • outputFile and inputFile represent the file stream objects
    • Actual file names are "someOutputFileName" and "someInputFileName" – inside double quotes
    • Place file extensions such as .dat, .dta, or .txt onto the end of actual filename when it is created

    File Streams (Continued)

    • Use Write() or WriteLine() with the instantiated stream object:
      • outputFile.WriteLine("This is the first line in a text file");
    • Use Read() or ReadLine() with the instantiated stream object:
      • string inValue = inputFile.ReadLine();### FileStream Class
    • The FileStream class is used to work with file streams and supports reading, writing, and positioning (if the device where the file is located supports these operations).
    • The FileStream class inherits from the Stream class and supports all of its methods and properties.
    • In its constructor, it is set:
      • File name
      • Way to open the file (FileMode)
      • Access mode (FileAccess)
      • Access for competing users (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 not by Notepad.
    • A program is needed to interpret the file contents.

    BinaryWriter Class

    • Instantiates an object of the FileStream and BinaryWriter classes.
    • FileStream filStream;
    • BinaryWriter binWriter;
    • BinaryWriter object is wrapped around the FileStream object.

    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.
    • Three different read methods were invoked to read data from the file:
      • ReadInt32()
      • ReadDecimal()
      • ReadString()

    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

    • File class:
      • Provides 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.
    • FileInfo class:
      • Provides 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 FileInfo class provides these methods by instance.

    Directory and DirectoryInfo Classes

    • Directory class:
      • Provides 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.
    • DirectoryInfo class:
      • Provides 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 DirectoryInfo class provides these methods by instance.

    Path Class

    • The System.IO.Path class provides functionality for working with paths.
    • More important properties and methods:
      • DirectorySeparatorChar
      • Combine(...)
      • GetExtension(...)
      • GetFileName(...)
      • GetTempFileName(...)### Environment Special Folders
    • Environment.SpecialFolder.MyDocuments returns the path to the My Documents folder.
    • Environment.SpecialFolder.DesktopDirectory returns the path to the Desktop folder.
    • Environment.SpecialFolder.Favorites returns the path to the Favorites folder.

    Disadvantages of Text Files

    • Data in text files is easily readable and not secure.
    • Converting each field to text and combining fields with delimiters can be cumbersome.

    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.

    Object Serialization in C#

    • Object serialization allows entire objects to be written to or read from a file.
    • Serialized objects can be read from a file and deserialized.

    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 this representation from a file and reconstructs the original object.

    Serializable Class Requirements

    • A class marked with the [Serializable] attribute must have all instance variables that are also serializable.
    • By default, all C# simple data types are serializable, including strings.
    • If a class contains fields that are more complex data types, you must check the declaration of those classes to ensure they are serializable.

    Serialization Example

    • A serializable class can be written to a file using the BinaryFormatter class.
    • The serialized object can be read from the file and deserialized using the BinaryFormatter class.

    Creating a Sequential-Access File Using Object Serialization

    • The classes for objects that we wish to serialize must include the [Serializable] attribute in their declarations or must implement interface ISerializable.
    • In a serializable class, you must ensure that every instance variable of the class is also serializable.
    • Array objects are serializable by default, but if the array contains references to other objects, those objects may or may not be serializable.

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    This quiz covers the basics of working with files in C# programming, including data storage and retrieval. Learn about persistent data and how computers store files on secondary storage devices.

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