C# StreamWriter
last modified July 5, 2023
C# StreamWriter tutorial shows how to write text files in C# with StreamWriter. C# tutorial is a comprehensive tutorial on C# language.
Input & output in C# is based on streams. A Stream is an
abstract base class of all streams. A stream is an abstraction of a sequence of
bytes, such as a file, an input/output device, an inter-process communication
pipe, or a TCP/IP socket.
C# StreamWriter
StreamWriter writes characters to a stream in a particular encoding.
StreamWriter defaults to UTF-8 encoding unless specified otherwise.
C# StreamWriter example
The WriteLine method writes a new line to the stream. There
are several overloaded methods of WriteLine.
var path = "data.txt";
using var sw = new StreamWriter(path);
sw.WriteLine("old falcon");
sw.WriteLine("stormy night");
Console.WriteLine("data written to file");
The example writes two lines to the data.txt file.
using var sw = new StreamWriter(path);
A StreamWriter is created. The using keyword closes
the opened file at the end of the Main method.
sw.WriteLine("old falcon");
sw.WriteLine("stormy night");
Two lines are written to the stream.
$ dotnet run data written to file $ cat data.txt old falcon stormy night
C# StreamWriter write formatted string
We can write formatted strings with the WriteLine, similarly to
string.Format.
Visit C# String Format tutorial to learn more about string formatting in C#.
using FileStream fs = File.Create("data.txt");
using var sw = new StreamWriter(fs);
int n = 3;
string word = "hawks";
sw.WriteLine("There are {0} {1} in the sky", n, word);
Console.WriteLine("data written to file");
The example writes a formatted line to the file.
using FileStream fs = File.Create("data.txt");
A FileStream is created with File.Create.
using var sw = new StreamWriter(fs);
A StreamWriter is generated by passing the FileStream
to the constructor of the StreamWriter.
int n = 3;
string word = "hawks";
sw.WriteLine("There are {0} {1} in the sky", n, word);
A formatted line is written to the stream. The {0} and
{1} placeholders are replaced with the contents of the
n and word
variables.
C# StreamWriter append text
We can create a StreamWriter that will append text to the file.
public StreamWriter(string path, bool append);
This constructor initializes a new instance of the StreamWriter
class for the specified file by using the default encoding and buffer size. If
the file exists, it can be either overwritten or appended to. If the file does
not exist, the constructor creates a new file.
var path = "words.txt";
using var sw = new StreamWriter(path, true);
char[] data = {'h', 'a', 'w', 'k'};
sw.WriteLine(data);
Console.WriteLine("data appended to file");
The example appends a word to the words.txt file.
using var sw = new StreamWriter(path, true);
The StreamWriter is opened in the Append mode by passing true
as the second parameter to the constructor.
char[] data = {'h', 'a', 'w', 'k'};
sw.WriteLine(data);
This overloaded method of WriteLine writes an array of characters
to the stream.
Source
StreamWriter class - language reference
In this article we have read text files in C# with StreamWriter.
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