{"id":1193,"date":"2023-03-28T10:59:47","date_gmt":"2023-03-28T03:59:47","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=1193"},"modified":"2023-03-28T10:59:53","modified_gmt":"2023-03-28T03:59:53","slug":"csharp-write-text-files","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-file\/csharp-write-text-files\/","title":{"rendered":"C# Write Text Files"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn various techniques to write text files in C# using the File<\/code> static methods and StreamWriter<\/code> class.<\/p>\n\n\n\n

Writing all text into a text file<\/h2>\n\n\n\n

The File.WriteAllText<\/code>()<\/code> method creates a new file, writes the contents to it, and then closes the file:<\/p>\n\n\n

public<\/span> static<\/span> void<\/span> WriteAllText<\/span> (string<\/span> path, string<\/span>? contents<\/span>)<\/span>;<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
If the file specified by the path exists, the WriteAllText()<\/code> method overwrites it. In other words, the contents of the existing file will be replaced by the contents.<\/p>\n\n\n\n
The following program demonstrates how to use File.WriteAllText<\/code>()<\/code> method to write all text into a text file:<\/p>\n\n\n
using<\/span> static<\/span> System.Console;\n\nstring<\/span> path = @\"C:\\temp\\readme.txt\"<\/span>;\nstring<\/span> contents = \"Hello\\nGoodbye\"<\/span>;\n\nFile.WriteAllText(path, contents);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
The readme.txt<\/code> will look like the following:<\/p>\n\n\n
Hello\nGoodbye<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
This program writes the string “Hello” and “Goodbye” to the readme.txt<\/code> file located in the “C:\\temp” directory.<\/p>\n\n\n\n
If the C:\\temp directory does not exist, the WriteAllText()<\/code> method throws a DirectoryNotFoundException<\/code>. <\/p>\n\n\n\n
For example, the following program attempts to write text to a file readme.txt<\/code> located in the C:\\temp1<\/code> directory. Since the directory C:\\temp1<\/code> doesn’t exist, the program shows a message provided by the DirectoryNotFoundException<\/code> object:<\/p>\n\n\n
using<\/span> static<\/span> System.Console;\n\nstring<\/span> path = @\"C:\\temp1\\readme.txt\"<\/span>;\nstring<\/span> contents = \"Hello\\nGoodbye\"<\/span>;\n\ntry<\/span>\n{\n    File.WriteAllText(path, contents);\n}\ncatch<\/span> (DirectoryNotFoundException e)\n{\n    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 a part of the path 'C:\\temp1\\readme.txt'<\/span>.<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
To check if the text file exists before writing the contents to it, you can use the File.Exists<\/code>()<\/code> method like this:<\/p>\n\n\n
using<\/span> static<\/span> System.Console;\n\nstring<\/span> path = @\"C:\\temp\\readme.txt\"<\/span>;\nstring<\/span> contents = \"Hello\\nGoodbye\"<\/span>;\n\nif<\/span> (!File.Exists(path))\n{\n    File.WriteAllText(path, contents);\n}\nelse<\/span>\n{\n    WriteLine($\"The file {path}<\/span> alrady exists\"<\/span>);\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
The file C:\\temp\\readme.txt alrady exists<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Writing one or more strings into a text file<\/h2>\n\n\n\n
To write one or more strings into a text file, you use the File.WriteAllLines<\/code><\/code>()<\/code><\/code> method. The File.WriteAllLines<\/code><\/code>()<\/code><\/code> method creates a new file, writes one or more strings to the file, and then closes the file:<\/p>\n\n\n
public<\/span> static<\/span> void<\/span> WriteAllLines<\/span> (\n   string<\/span> path, \n   string<\/span>[] contents\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
string<\/span> path = @\"C:\\temp\\readme.txt\"<\/span>;\n\nstring<\/span>[] lines = new<\/span>[] {\n    \"Hello\"<\/span>,\n    \"Hi\"<\/span>,\n    \"Hey\"<\/span>\n};\n\nFile.WriteAllLines(path, lines);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
The readme.txt<\/code> file will look like this:<\/p>\n\n\n
Hello\nHi\nHey<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Writing into a text file using StreamWriter<\/h2>\n\n\n\n
When you have a large amount of text data that you want to write into a text file in sequential order, you can use StreamWriter<\/code>. For example:<\/p>\n\n\n
string<\/span> path = @\"C:\\temp\\readme.txt\"<\/span>;\n\n\/\/ in practice, the greetings is very big<\/span>\nstring<\/span>[] greetings = new<\/span>[] { \"Hello\"<\/span>, \"Hi\"<\/span>, \"Hey\"<\/span> };\n\nvar<\/span> fs = new<\/span> FileStream(path, FileMode.Open);\nvar<\/span> stream = new<\/span> StreamWriter(fs);\n\nforeach<\/span> (var<\/span> greeting in<\/span> greetings)\n{\n    \/\/ write each line to the stream<\/span>\n    stream.WriteLine(greeting);\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
How it works.<\/p>\n\n\n\n
First, define a string variable named “path” and assigns it the value of the file path C:\\temp\\readme.txt<\/code> where we want to write the text.<\/p>\n\n\n\n
Next, create an array of strings named “greetings” that has three different strings – \"Hello\",<\/code> \"Hi\"<\/code>, and \"Hey\"<\/code>.<\/p>\n\n\n\n
Then, create a FileStream<\/code> object named fs that open the file specified by the path with the mode FileMode<\/code>.Open. <\/p>\n\n\n\n
After that, create a StreamWriter<\/code> object that writes text to the file using the FileStream<\/code> object.<\/p>\n\n\n\n
Finally, iterate the greetings array and write each element into the file using the StreamWriter<\/code> object.<\/p>\n\n\n\n
Writing into a text file asynchronously<\/h2>\n\n\n\n
To write data into a text file asynchronously, you can use the async<\/a><\/code> versions of the WriteAllText<\/code> and WriteAllLines()<\/code> methods:<\/p>\n\n\n
public<\/span> static<\/span> Task WriteAllTextAsync<\/span> (string<\/span> path, string<\/span>? contents, CancellationToken cancellationToken = default<\/span><\/span>)<\/span>;\npublic<\/span> static<\/span> Task WriteAllLinesAsync<\/span> (string<\/span> path, IEnumerable<string<\/span>> contents, CancellationToken cancellationToken = default<\/span><\/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> path = @\"C:\\temp\\readme.txt\"<\/span>;\n\nstring<\/span>[] greetings = new<\/span>[] {\n    \"Hello\"<\/span>,\n    \"Hi\"<\/span>,\n    \"Hey\"<\/span>\n};\n\nawait<\/span> File.WriteAllLinesAsync(path, greetings);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, we use the WriteAllLinesAsync()<\/code> method to asynchronously write the array of strings into a text file. <\/p>\n\n\n\n
Note that we use the await<\/code> keyword to wait for the WriteAllLinesAsync()<\/code> method to complete.<\/p>\n\n\n\n
Summary<\/h2>\n\n\n\n
    \n
  • Use the File.WriteAllText<\/code>()<\/code> method to write all text into a text file.<\/li>\n\n\n\n
  • Use the File.WriteAllTextAsync<\/code>()<\/code> method to write text data into a text file asynchronously.<\/li>\n\n\n\n
  • Use the File.WriteAllLines<\/code>()<\/code> method to write an array of strings into a text file.<\/li>\n\n\n\n
  • Use the File.WriteAllLinesAsync<\/code>()<\/code> method to write an array of strings into a text file asynchronously.<\/li>\n\n\n\n
  • Use the StreamWriter<\/code> to write a large amount of text into a text file.<\/li>\n<\/ul>\n
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