{"id":1185,"date":"2023-03-28T09:52:12","date_gmt":"2023-03-28T02:52:12","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=1185"},"modified":"2023-03-28T10:04:48","modified_gmt":"2023-03-28T03:04:48","slug":"csharp-read-text-files","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-file\/csharp-read-text-files\/","title":{"rendered":"C# Read Text Files"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn various techniques to read text files in C# using File.ReadAllText<\/code>()<\/code>, File.ReadAllText<\/code>Async()<\/code>, File.ReadAllLines<\/code>()<\/code>, File.ReadAllLines<\/code>Async()<\/code> method, and FileStream<\/code> class.<\/p>\n\n\n\n

C# provides various ways to allow you to read text files effectively. We’ll create a readme.txt<\/code> file in the C:\\temp\\<\/code> directory for the demonstration.<\/p>\n\n\n\n

The readme.txt<\/code> file has two lines:<\/p>\n\n\n

Hello\nBye<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Reading a text file into a string<\/h2>\n\n\n\n
If a text file is small, you can read all the file contents into a string using the File.ReadAllText<\/code>()<\/code> static method<\/a>:<\/p>\n\n\n
public<\/span> static<\/span> string<\/span> ReadAllText<\/span>(string<\/span> path<\/span>)<\/span>;<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
The File.ReadAllText<\/code>()<\/code> method opens a text file, reads all the text of the file into a string, and then closes the file.<\/p>\n\n\n\n
For example, the following program uses the File.ReadAllText<\/code>()<\/code> method to read the contents in the readme.txt<\/code> file and writes the text to the console:<\/p>\n\n\n
string<\/span> contents = File.ReadAllText(@\"C:\\temp\\readme.txt\"<\/span>);\nConsole.WriteLine(contents);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
If the file is not found, the File.ReadAllText<\/code>()<\/code> raises a FileNotFoundException<\/code><\/code>. For example, the following program attempts to read a file readme1.txt<\/code> from the C:\\temp\\<\/code> directory, which doesn’t exist and handles the FileNotFoundException<\/code><\/code>:<\/p>\n\n\n
try<\/span>\n{\n    string<\/span> contents = File.ReadAllText(@\"C:\\temp\\readme1.txt\"<\/span>);\n    Console.WriteLine(contents);\n}\ncatch<\/span> (FileNotFoundException e)\n{\n    Console.WriteLine(e.Message);\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Could not find file 'C:\\temp\\readme1.txt'<\/span>.<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Reading a text file into an array of string<\/h2>\n\n\n\n
If you want to process a small text file line by line, you can read its contents into an array<\/a> of strings, where each array element stores a line in the text file. <\/p>\n\n\n\n
To read the contents of a text file into an array of strings, you use the File.ReadAllLines<\/code>()<\/code> method:<\/p>\n\n\n
public<\/span> static<\/span> string<\/span>[] ReadAllLines<\/span> (string<\/span> path<\/span>)<\/span>;<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
For example:<\/p>\n\n\n
string<\/span>[] lines = File.ReadAllLines(@\"C:\\temp\\readme.txt\"<\/span>);\nforeach<\/span> (var<\/span> line in<\/span> lines)\n{\n    Console.WriteLine(line.ToUpperInvariant());\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
HELLO\nBYE<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Reading a large text file line by line<\/h2>\n\n\n\n
If a text file is large, reading the entire text file into a string or an array of strings is not memory-optimized. <\/p>\n\n\n\n
In this case, you can read the contents of a text file using a stream and process the contents line by line.<\/p>\n\n\n\n
A stream represents a flow of data that you can read from. To read data from a file, you can create a FileStream<\/code> and use a StreamReader<\/code> to read data from the FileStream<\/code>.<\/p>\n\n\n\n
Here are the steps:<\/p>\n\n\n\n
First, create a FileStream<\/code><\/code> with the FileMode<\/code>.Open using the FileStream<\/code><\/code> class:<\/p>\n\n\n
using<\/span> var<\/span> fs = new<\/span> FileStream(path, FileMode.Open);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Second, create a new StreamReader<\/code> to read the contents of the FileStream<\/code>:<\/p>\n\n\n
using<\/span> var<\/span> reader = new<\/span> StreamReader(fs);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Third, read the line from the StreamReader<\/code><\/code> till the end of the stream. To check if the program reaches the end of the stream, you use the reader.EndOfStream<\/code> property. To read a line from a StreamReader<\/code><\/code>, you use the ReadLine()<\/code> method.<\/p>\n\n\n\n
The following program demonstrates how to read the contents of the readme.txt<\/code> line by line using a FileStream<\/code> and StreamReader<\/code>:<\/p>\n\n\n
using<\/span> static<\/span> System.Console;\n\nusing<\/span> var<\/span> fs = new<\/span> FileStream(@\"C:\\temp\\readme.txt\"<\/span>, FileMode.Open);\nusing<\/span> var<\/span> reader = new<\/span> StreamReader(fs);\n\nwhile<\/span> (!reader.EndOfStream)\n{\n    var<\/span> line = reader.ReadLine();\n    WriteLine(line?.ToUpperInvariant());\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
HELLO\nBYE<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
The program works fine but the code looks quite verbose. To make it more concise, you can use the File.OpenText<\/code>()<\/code> static method. <\/p>\n\n\n\n
The File.OpenText<\/code>()<\/code> method accepts a path and returns a new instance of the StreamReader<\/code> class. Here’s the revised version of the above program:<\/p>\n\n\n
using<\/span> static<\/span> System.Console;\n\nusing<\/span> var<\/span> reader = File.OpenText(@\"C:\\temp\\readme.txt\"<\/span>);\n\nwhile<\/span> (!reader.EndOfStream)\n{\n    var<\/span> line = reader.ReadLine();\n    WriteLine(line?.ToUpperInvariant());\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
So these two lines:<\/p>\n\n\n
using<\/span> var<\/span> fs = new<\/span> FileStream(@\"C:\\temp\\readme.txt\"<\/span>, FileMode.Open);\nusing<\/span> var<\/span> reader = new<\/span> StreamReader(fs);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
become one:<\/p>\n\n\n
using<\/span> var<\/span> reader = File.OpenText(@\"C:\\temp\\readme.txt\"<\/span>);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Read all text into a string asynchronously<\/h2>\n\n\n\n
To read all contents of a text file into a string asynchronously, you use the File.ReadAllTextAsync<\/code>()<\/code> method:<\/p>\n\n\n
public<\/span> static<\/span> Task<string<\/span>> ReadAllTextAsync<\/span> (\n    string<\/span> path, \n    CancellationToken cancellationToken = default<\/span>\n<\/span>)<\/span>;<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
For example:<\/p>\n\n\n
using<\/span> static<\/span> System.Console;\n\nvar<\/span> text = await<\/span> File.ReadAllTextAsync(@\"C:\\temp\\readme.txt\"<\/span>);\nWriteLine(text);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Hello\nBye<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Since the File.ReadAllTextAsync<\/code>()<\/code> method returns a Task<String><\/code>, you need to use await<\/a><\/code> keyword to wait for the task to complete and get the string result.<\/p>\n\n\n\n
Similarly, you can read all lines of a text file into an array of strings asynchronously using the File.ReadAllLineAsync<\/code>()<\/code> static method:<\/p>\n\n\n
public<\/span> static<\/span> Task<string<\/span>[]> ReadAllLinesAsync (\n   string<\/span> path,\n   CancellationToken cancellationToken = default<\/span>\n);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
For example:<\/p>\n\n\n
using<\/span> static<\/span> System.Console;\n\nvar<\/span> lines = await<\/span> File.ReadAllLinesAsync(@\"C:\\temp\\readme.txt\"<\/span>);\nforeach<\/span> (var<\/span> line in<\/span> lines)\n{\n    WriteLine(line);\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Reading a text file with a specified encoding<\/h2>\n\n\n\n
By default, each of the ReadAllText<\/code>, ReadAllLines<\/code>, ReadAllTextAsync<\/code>, and ReadAllLineAsync<\/code> method has an overload that allows you to specify the encoding applied to the text of the file:<\/p>\n\n\n
public<\/span> static<\/span> string<\/span> ReadAllText<\/span> (string<\/span> path, Encoding encoding<\/span>)<\/span>;\npublic<\/span> static<\/span> string<\/span>[] ReadAllLines<\/span> (string<\/span> path, Encoding encoding<\/span>)<\/span>;\npublic<\/span> static<\/span> Task<string<\/span>> ReadAllTextAsync<\/span> (string<\/span> path, Encoding encoding, CancellationToken cancellationToken = default<\/span><\/span>)<\/span>;\npublic<\/span> static<\/span> Task<string<\/span>[]> ReadAllLinesAsync(string<\/span> path, Encoding encoding, CancellationToken cancellationToken = default<\/span>);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
 In this syntax, the Encoding<\/code> class belongs to the System.Text<\/code> namespace.<\/p>\n\n\n\n
Summary<\/h2>\n\n\n\n
    \n
  • Use the File.ReadAllText<\/code>()<\/code> method to read the contents of a small text file into a string.<\/li>\n\n\n\n
  • Use the File.ReadAllLines<\/code>()<\/code> method to read the contents of a small text file into an array of strings.<\/li>\n\n\n\n
  • Use the File.ReadAllTextAsync<\/code>()<\/code> method to read the contents of a small text file into a string asynchronously.<\/li>\n\n\n\n
  • Use the File.ReadAllLinesAsync<\/code>()<\/code> method to read all lines of a text file into an array of strings asynchronously.<\/li>\n<\/ul>\n
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