Streams and Text Files
Telerik Academy Alpha
Table of contents
What is a stream?
What is a stream?
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A stream is an abstraction of a sequence of bytes.
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Can be accessed in sequential order (pipe with water flowing through it)
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Text files, Images, Network access
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Two main streams
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Input stream (read data)
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Output stream (write date)
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System.IO namespace in C#
What is a stream?
Program
Input stream
Output stream
Input Source (keyboard, file, network, etc.)
Output Sink (console, file, network, etc.)
What is a stream?
- Stream must be open when needed
- and closed when you don't need it anymore
- It is the programmer responsibility
- can be done with using() block
Stream fileStream = new FileStream("../../../test.jpg", FileMode.Open, FileAccess.Read);
// Do some operations with the file stream
// Close the stream
fileStream.Close();
// The stream is automatically closed
using (fileStream = new FileStream("../../../test.jpg", FileMode.Open, FileAccess.Read))
{
// Do some operations with the file stream
}
File streams, readers, writers
File streams
- With FileStream you can read/write bytes from file
// Write new string to file
string str = "Telerik Academy Alpha";
using(FileStream fileStream = new FileStream("../../../test.txt", FileMode.Open))
{
for (int i = 0; i < str.Length; i++)
{
fileStream.WriteByte((byte)str[i]);
}
}
// Read all chars
using (FileStream fileStream = new FileStream("../../../test.txt", FileMode.Open))
{
for (int i = 0; i < fileStream.Length; i++)
{
Console.Write((char)fileStream.ReadByte());
}
}
File streams and writers/readers
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StreamReader/Writer vs FileStream
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streams handle bytes
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readers/writers handle characters
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var reader = new StreamReader("../../../test.txt");
Console.WriteLine((char)reader.Read()); // output: T
// Should close it before using it again below
// Otherwidse the file will be in use
reader.Close();
FileStream fileStream = new FileStream("../../../test.txt", FileMode.Open);
Console.WriteLine((char)fileStream.ReadByte()); // output: T
fileStream.Close();
Readers/writers
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StreamReader/Writer
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Reader (byte[] to string)
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Writer (string to byte[])
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using (var reader = new StreamReader("../../../test.txt"))
{
Console.WriteLine(reader.ReadLine()); // Telerik Academy
// More methods: reader.ReadToEnd();
}
using (var writer = new StreamWriter("../../../test.txt"))
{
writer.WriteLine("Telerik Academy Alpha"); // Writes to text file
// More methods: writer.Write();
}
Combine them
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Combine Stream and StreamReader/Writer
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StreamReader/Writer accepts stream or path
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using (FileStream fileStream = new FileStream("../../../test.txt", FileMode.Open))
{
var reader = new StreamReader(fileStream);
Console.WriteLine(reader.ReadLine()); // Telerik Academy
}
Files
Text Files
TextFiles
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You could read or write text files with wrappers over a stream
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Both StreamReader/Writer and File classes are wrappers over streams
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Both could read all lines of text from a file
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StreamReader/Writer gives more control
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It could read/write file without loading the whole file
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File makes your code shorter and more understandable
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TextFiles
using (StreamReader reader = new StreamReader("../../../test.txt"))
{
Console.WriteLine(reader.ReadToEnd());
}
Console.WriteLine(File.ReadAllText("../../../test.txt"));
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Below code is reading all the text from a file with the two options
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StreamReader
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File
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TextFiles
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StreamReader/Writer could read/write to/from files line by line
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This is very useful for certain situations
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You should choose which class to use (File or StreamReader/Writer) depending on your code requirements
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There is no right or wrong
Other Files
Copy file
// Copy an image
// This reads the file as a byte array
// You could use any other method or class
byte[] arr = File.ReadAllBytes("../../../test.jpg");
// This writes the file to the file system
File.WriteAllBytes("../../../test-copy.jpg", arr);
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You can copy any file
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Image
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Text file
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pdf
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etc.
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Modify file
// This will read the file as byte[]
// then it will save another file with bytes only at the even positions
// if the file is an image/pdf or another type of file it will be corrupted
// but if it is a text file it will have missing parts
byte[] arr = File.ReadAllBytes("../../../test.pdf");
List<byte> list = new List<byte>();
for (int i = 0; i < arr.Length; i++)
{
if (i % 2 == 0)
{
list.Add(arr[i]);
}
}
File.WriteAllBytes("../../../test-part.pdf", list.ToArray());
Questions?
[C#] Streams and files
By telerikacademy
[C#] Streams and files
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