How to Append Lines to a File Using StreamWriter in C#?

Using StreamWriter to Add Lines to a File in C#

This guide explains how to append lines to an existing file using C#'s StreamWriter class. A common mistake is to unintentionally overwrite the file instead of appending. The solution lies in correctly utilizing the StreamWriter constructor.

The standard StreamWriter constructor, by default, overwrites any pre-existing file content. To append new lines instead, you must use the append flag. Here's how:

<code class="language-csharp">new StreamWriter("c:\file.txt", true);</code>

Setting the second argument (true) enables appending mode. StreamWriter will now add new lines to the end of the file.

For enhanced readability (available in C# 4 and later), use this alternative syntax:

<code class="language-csharp">new StreamWriter("c:\file.txt", append: true);</code>

By incorporating this change, your code will successfully append lines, preserving existing file content and extending it with each execution.

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