PRE FI EVENT DRIVEN

Streams

Handling Files Streams represent a source that provides a sequence of bytes, such as a file, an input/output (I/O) device, an interprocess communication pipe, or a TCP/IP socket (Harwani, 2015, p. 454).

Two (2) Types of Streams

Output streams – It refers to a printer, remote server location, or a printer where the data is written.
Input streams – It refers to a file or any source where the data can be read and assigned to the memory variables in the program.

In C#, the System.IO namespace contains classes that allow to write and read files. This namespace needs to be included in all programs that use streams. All files are byte-oriented, meaning the data is written or read into the files in terms of bytes.

FileStream

It is a class that is used to create a byte-oriented stream attached to a file. The code to be used for creating a FileStream object is

FileStream(string filename,FileMode mode)

The mode parameter specifies how the file needs to be opened. The options for FileMode are as follows:

FileMode.Create – It creates a new output file, which will be overwritten if a file already exists.
FileMode.CreateNew – It creates a new output file that is not existing.
FileMode.Open – It opens an existing file.
FileMode.OpenOrCreate – It opens an existing. If not, it creates a new one.
FileMode.Truncate – It opens an existing file and truncates the content that already exists.

The FileStream constructor is used to open a file that has access to read or write. This class also contains the following methods to perform read and write operations:

ReadByte() – This method reads a single byte from a file and returns as an integer value.
Read() – This method reads the specified number of bytes from a file into an array.
WriteByte() – It writes the specified byte into the file.
Write() – It writes an array of bytes into the file.
Flush() – This method instantly writes the data into the file.
void Close() – This method closes the file, releasing the system resources that are allocated to it.

Reading Files To access a file randomly, position the file pointer inside the file at the required location. A file pointer determines the location of the next read/write operation to take place on the file. The method used to relocate the file pointer in the file

is Seek (Harwani, 2015, p. 462). Seek() is a method that allows setting the file position indicator of file pointer to the

preferred location in the file. The syntax for this method is

long Seek(long n, SeekOrigin location)

The file pointer can get or set the position using the Position property of Stream class. Aside from the Position

property, these properties are commonly used:

bool CanRead – It returns true if the stream can be read.
bool CanSeek – It returns true if the stream supports position requests.
bool CanTimeout – It returns true if the stream can time out.
bool CanWrite – It returns true if the stream can be written.
long length – It contains the size of the stream.
int ReadTimeout – It indicates the time before a timeout occurs for read operations.
int WriteTimeout – It indicates the time before a timeout occurs for write operations.

Performing Character-Based File I/O

To perform a character-based file for managing text files, use character streams to read and write into the file. Since, internally, each file consists of bytes, the FileStream is wrapped inside either a StreamReader or a StreamWriter. These classes automatically convert a byte stream into a character stream, and vice versa. (Harwani, 2015, p. 468)

StreamWriter writes characters to a stream and contains several constructors, such as the following:

SteamWriter(Stream stream) – It is used to create a character-based output stream.
StreamWriter(string fileName) – It is used to open a file directly.

This class contains the following common methods:

Close() – It closes the file.
Flush() – It instantly saves the file content from buffer to memory
Write() – Using a File stream class, this writes into the specified file.
WriteLine() – Line by line, it writes into a file.

StreamReader is a class that reads characters from a byte stream. It defines the following constructors:

StreamReader(Stream stream) - It is the name of an open stream such I/O devices or a file.
StreamReader(string fileName) – It specifies the name of the file to open.

This class also contains the following common methods:

Flush() – From buffer to memory, it instantly saves the file content.
Close() – It closes the file and is mandatory to this class.
Read() – From the file stream, it reads the content.
ReadLine() – From the given file stream, it reads the content line by line.
ReadToEnd() – From the current location until the end of the stream, it reads all characters.
Peek() – It returns the value in the stream without moving the file pointer.
Seek() – Sets the file pointer at the desired position in a file.

IT1811

.NET Assemblies

Private Assemblies

Assemblies are files that contain compiled code targeted at the .NET Framework. These are basically physical packages

meant for distributing code. The .NET classes are actually contained in several assemblies (Harwani, 2015, p. 621).

An assembly has two (2) sections:

Metadata – It includes information about the data types of the program that are being used.
Manifest – It holds the information of the assembly, which consists of the name, version number, and the type of mapping information.

An assembly also has two (2) file extensions:

.exe – for standalone applications
.dll – for reusable components.

.NET Frameworks’ core assemblies location can be found in C:\Windows\assembly.

Private Assembly

Simplest type of assembly
Can only be used within a software package that is intended to be used.
Two (2) private assemblies with the same class name are not a problem since the application can only see the classes that are mentioned in its private assemblies
Does not require registry entries

Shared Assemblies

These are libraries that other applications can commonly use. Security precautions are necessary when using a shared assembly since any other software can access a shared assembly.

Name Collision

It is a common problem in shared assembly wherein other classes or variables have the same name that matches with the other shared assembly.
A different form of the same assembly might overwrite the shared assembly, and the new version might be incompatible with the existing code.
Shared assemblies are giving a strong, unique name based on the private key cryptography to avoid name collision.

Global Assembly Cache (GAC)

It enables several applications to share shared assembly.
It is required to add the assembly to the special directory.
It is a centralized storage location for .NET Assemblies.

Creating a Shared Assembly

These are the steps to creating a shared assembly:

Create a project containing a class file. The class file contains the methods and properties that you want other applications to access.
Generate a strong name for the project. The strong name is saved in a strong key filename (e.g., ShareAssemblyMessageKeyFile). The strong key file is created named ShareAssemblyMessageKeyFile.snk and located at the solutions explorer.
Specify the key filename in the project by indicating its strong key filename in the AssemblyInfo.cs file.
Compile the project to generate an assembly. The assembly is generated with the extension .dll.

REFERENCES:

Deitel, P. & Deitel, H. (2015). Visual C# 2012 how to program (5^th ed.). USA: Pearson Education, Inc. Gaddis, T. (2016). Starting out with Visual C# (4^th ed.). USA: Pearson Education, Inc.

Harwani, B. (2015). Learning object-oriented programming in C# 5.0. USA: Cengage Learning PTR. Miles, R. (2016). Begin to code with C#. Redmond Washington: Microsoft Press.

Doyle, B. (2015). C# programming: from problem analysis to program design (5^th ed.). Boston, MA: Cengage Learning.

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