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Chapter 17

Files and Streams

Files Used for long-term retention of large amounts of data, even after the program that created the data terminates. A group of related records
Persistent Data Data maintained in files
Secondary Storage Devices Magnetic disks, optical disks, flash memory and magnetic tapes. Computers store files on secondary storage devices
Bits The smallest data item that computers support. Can assume either the value 0 or the value 1
Characters Digits, letters, and special symbols
Decimal Digits 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9
Letters A-Z and a-z
Special Symbols $, @, %, &, *, (, ), -, +, ", :, ?, /
Character Set The set of all characters used to write programs and represent data items on a particular computer
Bytes Composed of eight bits
Fields A group of characters that convey meaning. Just as characters are composed of bits, fields are composed of characters. Ex: Judy
Data Hierarchy Data items processed by computers form a data hierarchy, in which data items become larger and more complex in structure as we progress from bits to characters to fields to larger data aggregates
Records Composed of several related fields. For example, a record for a particular employee might include... 1. ID number... 2. Name... 3. Address... 4. Hourly Pay Rate...Each field is associated with same employee
Record Key Identifies a record as belonging to a particular person or entity and distinguishes that record from all others. To facilitate the retrieval of specific records from a file, at least one field in each record is chosen as a record key
Sequential File A common file organization in which records typically are stored in order by a record-key field
Database Related data are often stores in databases
Database Management System(DBMS) A collection of programs designed to create or manage databases
Streams C# views each file as a sequential stream of bytes
End-Of-File Marker Each file ends either with an end-of-file marker or at a specific byte number that's recorded in a system-maintained administrative data structure
Console.Out, Console.In, Console.Error When a console app executes, the runtime environment creates three stream objects that are accessible via properties Console.out, Console.In, Console.Error. These objects use streams to facilitate communication between a program and a file or device
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
System.I0 Namespace Includes stream classes such as StreamReader(for text input form a file), StreamWriter(for text output to a file), and FileStream(for both input and output to file). These stream classes inherit from abstract classes TextReader, TextWriter, and Stream
Stream Abstract class Stream provides functionality for representing streams as bytes. Classes FileStream, MemoryStream, and BufferedStream(all from namespace System.I0) inherit from class Stream
Class FileStream Can be used to write data to and read data from files
Class MemoryStream Enables the transfer of data directly to and from memory - this is much faster than reading and writing to external devices
Class BufferedStream Uses buffering to transfer data to or from a stream
Buffering An I/O performance-enhancement technique in which each output operation is directed to a region in memory, called a buffer, that's large enough to hold the data from many output operations
Physical Output Operation Then actual transfer to the output device is performed in one large physical output operation each time the buffer fills
Logical Output Operations The output operations directed to the output buffer in memory
Classes File and Directory Enable programs to manipulate files and directories on disk
Class File Can determine information about files and can be used to open files for reading or writing
1. File Class static Methods(partial list) 1. Method[AppendText]..Description[Returns a StreamWriter that appends text to an existing file or creates a file if one does not exist]... 2. Method[Copy]..Description[Copies a file to a new file]...
2. File Class static Methods(partial list) 3. Method[Create]..Description[Creates a file and returns its associated Filestream]... 4. Method[CreateText]..Description[Creates a text file and returns its associated StreamWriter]...
3. File Class static Methods(partial list) 5. Method[Delete]..Description[Deletes the specified code]... 6. Method[Exists]..Description[Returns true if the specified file exists and false otherwise]...
4. File Class static Methods(partial list) 7. Method[GetCreationTime]..Description[Returns a DateTime object representing when the file was created]... 8. Method[GetLastAccessTime]..Description[Returns a DateTime object representing when the file was last accessed]...
5. File Class static Methods(partial list) 9. Method[GetLastWriteTime]..Description[Returns a DateTime object representing when the file was last modified]... 10. Method[Move]..Description[Moves the specified file to a specified location]...
6. File Class static Methods(partial list) 11. Method[Open]..Description[Returns a FileStream associated with the specified file and equipped with the specified read/write permissions]... 12. Method[OpenRead]..Description[Returns a read-only FileStream associated with the specified file]...
7. File Class static Methods(partial list) 13. Method[OpenText]..Description[Returns a StreamReader associated with the specified file]... 14. Method[OpenWrite]..Description[Returns a write FileStream associated with the specified file]
Class Directory Provides capabilities for manipulating directories
1. Directory Class static Methods 1. Method[CreateDirectory]..Description[Creates a directory and returns its associated DirectoryInfo object which contains information about a directory]... 2. Method[Delete]..Description[Deletes the specified directory]...
2. Directory Class static Methods 3. Method[Exists]..Description[Returns true if the specified directory exists and false otherwise]... 4. Method[GetDirectories]..Description[Returns a string array containing the names of the subdirectories in the specified directory]...
3. Directory Class static Methods 5. Method[GetFiles]..Description[Returns a string array containing the names of the files in the specified directory]... 6. Method[GetCreationTime]..Description[Returns a DateTime object representing when the directory was created]...
4. Directory Class static Methods 7. Method[GetLastAccessTime]..Description[Returns a DateTime object representing when the directory was last accessed]... 8. Method[GetLastWriteTime]..Description[Returns a DateTime object representing when items were last written to the directory]...
5. Directory Class static Methods 9. Method[Move]..Description[Moves the specified directory to a specified location]
Dictionary A Dictionary(namespace System.Collections.Generic) is a collection of key-value pairs, in which each key has a corresponding value
Class Dictionary A generic class
Method ContainsKey Dictionary method ContainsKey determines whether the specified file-name extension has been placed in the Dictionary previously
Method Add Dictionary method Add inserts a new key-value pair into the Dictionary
Method ShowDialog Returns a DialogResult specifying which button(Save or Cancel) the user clicked to close the dialog
FileStream You can open files to perform text manipulations by creating object of class FileStream. Ex: FileStream output = new FileStream(fileName, FileMode.OpenOrCreate, FileAccess.Write);
Constant FileMode.OpenOrCreate(2nd FileStream Argument) Indicates that the FileStream object should open the file if it exists or create the file if it does not exist
StreamWriter The contents of an existing file are overwritten by the StreamWriter. Ex: fileWriter = new StreamWriter(output);. To preserve the original contents of a file, use FileMode.Append
Constant FileAccess.Write(3rd FileStream Argument) Indicates that the program can perform only write operations with the FileStream object
FileAccess.Read(3rd FileStream Argument) For read-only access
FileAccess.ReadWrite(3rd FileStream Argument) For read and write access
1. File-Position Pointer A FileStream object can reposition its file-position pointer(which contais the byte number of the next byte to be read from or written to the file) to any position in the file.
2. File-Position Pointer When a FileStream object is opened, its file-position pointer is set to byte position 0(beginning of the file)
Serialized Object An object represented as a sequence of bytes that includes the object's data, as well as information about the object's type and the types of data stored in the object.
Deserialized After a serialized object has been written to a file, it can be read from the file and deserialized - that is, the type information and bytes that represent the object and its data can be used to recreate the object in memory
Class BinaryFormatter Enables entire objects to be written to or read from a stream. Namespace System.Runtime.Serialization.Formatters.Binary
Method Serialize BinaryFormatter method Serialize writes an object's representation to a file
Method Deserialize BinaryFormatter method Deserialize reads this representation from a file and reconstructs the original object
SerilizationException An exception thrown by both method Deserialize and Serialize if an error occurs during serialization or deserialization. Both methods require a Stream object as a parameter so that the BinaryFormatter can access the correct stream
Created by: TimC#Programming
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