09 iec t1_s1_oo_ps_session_13

Object-Oriented Programming Using C#
Objectives

In this session, you will learn to:
Implement read and write in text files
Implement read and write in binary files
Implement the Windows File System
Describe exceptions

Ver. 1.0 Session 13 Slide 1 of 24

Implementing Reading and Writing in the Text Files

• The Stream class is used to read from and to write data in
the text files.
• It is an abstract class, which supports reading and writing
bytes into it.
• If data of a file is only text, then you can use the
StreamReader class and the StreamWriter class to
accomplish the reading and writing tasks, respectively.


StreamReader Class

• The StreamReader class is inherited from the abstract class
TextReader.
• The TextReader class represents a reader which can read
a series of characters.


StreamReader Class (Contd.)

• The following table describes some of the commonly used
methods of the StreamReader class.
Methods Description
Close Closes the object of StreamReader class and the underlying stream, and
releases any system resources associated with the reader
Peek Returns the next available character but does not consume it
Read Reads the next character or the next set of characters from the stream

ReadLine Reads a line of characters from the current stream and returns data as a
string

Seek Allows the read/write position to be moved to any position within the file


StreamWriter Class

• The StreamWriter class is inherited from the abstract class
TextWriter.
• The TextWriter class represents a writer, which can write
a series of characters.
methods of the StreamWriter class.
Methods Description

Close Closes the current StreamWriter object and the underlying stream

Flush Clears all buffers for the current writer and causes any buffered data to be
written to the underlying stream

Write Writes to the stream

WriteLine Writes data specified by the overloaded parameters, followed by end of
line


Implementing Reading and Writing in Binary Files

• In C#, you can directly display the contents of the file on the
screen.
• Binary read and write means that a number is written as a
float representation consuming four bytes of space.
• The BinaryReader and BinaryWriter classes are used
for reading and writing the binary data in to files.


BinaryReader Class

• The BinaryReader class is used to read binary data from
a file.
methods of the BinaryReader class.

Method Description
Close Closes the current reader and the underlying stream
Read Reads characters from the underlying stream and advances the current
position of the stream


BinaryWriter Class

• The BinaryWriter class is used to write binary data to a
stream.
methods of the BinaryWriter class.

Method Description

Close Closes the current BinaryWriter and the underlying stream

Seek Sets the position within the current stream

Write Writes a value to the current stream

Flush Clears all buffers for the current writer and causes any buffered data
to be written to the underlying device


Implementing the Windows File System

• The ability to browse and locate files and directories for a
specific directory is essential for many programming tasks.
• Using classes such as the DirectoryInfo and FileInfo
classes in combination is an efficient way to gather the
required information about files and directories in a specific
location.


DirectoryInfo Class

• The DirectoryInfo class is derived from the
FileSystemInfo class.
properties of the DirectoryInfo class.
Property Description
Gets or sets attributes associated with the current file. This property is inherited
Attributes
from FileSystemInfo.
Gets or sets CreationTime of the current file. This property is inherited from
CreationTime
FileSystemInfo.
Exists Gets a Boolean value indicating whether the directory exist or not.
Gets a string containing the file extension. This property is inherited from
Extension
FileSystemInfo.
Gets a string containing the full path of the directory. This property is inherited from
FullName
FileSystemInfo.
Gets the last accessed time of the directory. This property is inherited from
LastAccessTime
FileSystemInfo.
Name Gets a string containing the name of a given file.


DirectoryInfo Class (Contd.)

methods of the DirectoryInfo class.
Method Description
Create Creates a directory.
CreateSubdirectory Creates a subdirectory.
Delete Deletes a directory.
Returns the directories in the current directory after matching all the
GetDirectories
criteria. It also allows you to search subdirectories within directories.
GetFiles Returns the files in the current directory.


FileInfo Class

• The FileInfo class is derived from FileSystemInfo
class.
• The following table describes some commonly used
properties FileInfo class.
Property Description
Gets or sets attributes associated with the current file. This property is inherited from
Attributes
FileSystemInfo.
Gets or sets CreationTime of the current file. This property is inherited from
CreationTime
FileSystemInfo.
Directory Gets an instance of the directory which the file belongs to.
Exists Gets a boolean value indicating whether the file exists or not.
Extension Gets a string containing the file extension. This property is inherited from FileSystemInfo.
Gets a string containing the full path of the file. This property is inherited from
FullName
FileSystemInfo.
LastAccessTime Gets the last accessed time of the file. This property is inherited from FileSystemInfo.
Gets the time of the last written activity to the file. This property is inherited from
LastWriteTime
FileSystemInfo.
Length Gets the size of the file.
Name Gets a string containing the name of a given file.


FileInfo Class (Contd.)

methods of the FileInfo class.
Method Description
Create Creates a file
AppendText Appends a text to the file represented by the FileInfo object
Delete Deletes a file
Open Opens file
OpenRead Opens a file in read-only mode


Describing Exceptions

An exception is an erroneous situation that occurs during
program execution.
When an exception occurs in an application, the system
throws an error.
The error is handled through the process of exception
handling.


Types of Errors

There are three types of errors that can occur in the
application:
– Syntax errors: Occurs when statements are not constructed
properly, keywords are misspelled, or punctuation is omitted.
– Run-time errors: Occurs when an application attempts to
perform an operation, which is not allowed at runtime.
– Logical errors: Occurs when an application compiles and runs
properly but does not produce the expected results.

Let us understand the various types of errors in detail.


Syntax Errors

class Errors
{

Console.WriteLine(“Enjoy Errors”)

}

Semicolon is missing from Console.WriteLine statement


Run-Time Errors

class Errors

{
int Num1=0;
int Num2=20;
int Num3;
Num3=Num2/Num1;

Console.WriteLine(“The Result is {0}”,
Num3);
}

Division by zero has taken place


Logical Errors

class Errors
{
int Num1=10;
int Num2=2;
int Num3;
Num3=Num2/Num1;

Console.WriteLine(“The Result is
{0}”, Num3);
}
Expected result = 5

Present result = 0.2


Exception Classes

• There are many exception classes which are directly or
indirectly derived from the System.Exception class.
Some of these classes are:
– System.ApplicationException class
– System.SystemException class


Exception Classes (Contd.)

The hierarchy of the exception classes is displayed in the
following figure.

System.Exception

System.ApplicationException

System.SystemException


Exception Classes (Contd.)

• The System.SystemException acts as a base class for
all the predefined system exceptions. The following table
describes some of the classes derived from the
System.SystemException class.
Exception Classes Description

System.IO.IOException Handles I/O errors

System.IndexOutOfRangeException Handles errors generated when a method refers to an array
element, which is out of its bound
System.NullReferenceException Handles errors generated during the process of
dereferencing a null object
System.DivideByZeroException Handles errors generated during the process of dividing the
dividend with zero
System.InvalidCastException Handles errors generated during typecasting
System.OutOfMemoryException Handles memory allocation to the application errors


Summary

In this session, you learned that:
– The Stream class is used to read and write data to the text
files. It is an abstract class, which supports reading and writing
bytes into it.
– The StreamReader class is inherited from the abstract class
TextReader. The TextReader class represents a reader
which can read a series of characters.
– The StreamWriter class is inherited from the abstract class
TextWriter. The TextWriter class represents a writer,
which can write a series of characters.
– The BinaryReader class allows reading of binary data from a
file.
– The BinaryWriter class allows writing of binary data to a
stream.


Summary (Contd.)

– The DirectoryInfo class is derived from FileSystemInfo
class and it works on a specific directory and shows the
fullpath of the current directory.
– The FileInfo class is derived from FileSystemInfo class
and it works on a specific directory to display the list of all the
files.
– An exception is an erroneous situation that occurs during
program execution.
– A syntax error occurs when a compiler cannot compile the
code. This may happen when the statements are not
constructed properly, keywords are misspelled, or punctuation
is omitted.
– A run-time error occurs when an application attempts to
perform an operation that is not allowed.


Summary (Contd.)

A logical error occurs when an application compiles and runs
properly but does not produce the expected results.
Exceptional conditions arise when an operation cannot be
completed normally during the processing of C# statements
and expressions.


09 iec t1_s1_oo_ps_session_13

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