File.ReadAllText

Learn to read a text file all at once with File.ReadAllText.

Reading with File.ReadAllText

The File.ReadAllText method reads the entire content of a text file into a single string. It requires using System.IO;. Call: string text = File.ReadAllText("hello.txt");. If the file is missing, it throws FileNotFoundException.

This is the most practical way for small and medium files. Because the whole file is loaded into memory, very large files should use StreamReader instead. You can print the text with Console.WriteLine or split it into lines with Split.

Using and System.IO

File operations live in the System.IO namespace. Add using System.IO; at the top of your file. This lets you call File.ReadAllText, File.WriteAllText and similar methods directly.

File paths come in two flavors: relative (e.g. "data.txt") and absolute (e.g. "C:\\temp\\data.txt"). Backslashes are escaped: "\\". Forward slashes also work: "temp/data.txt" is cross-platform.

Exercise Read a file and print it

First create the file with File.WriteAllText("hello.txt", "Hello world");. Then read it back with File.ReadAllText and print with Console.WriteLine.

Show example solution

First write with File.WriteAllText("hello.txt", "Hello world");, then read with var text = File.ReadAllText("hello.txt");, finally print with Console.WriteLine(text);.
Example solution:
using System;
using System.IO;

class Program
{
    static void Main()
    {
        File.WriteAllText("hello.txt", "Hello world");
        var text = File.ReadAllText("hello.txt");
        Console.WriteLine(text);
    }
}

Test yourself

What does File.ReadAllText return?
```
File.ReadAllText("a.txt")
```
- string[] (array of lines)
- string (single text)
- byte[] (raw data)
- StreamReader
Show answer

string (single text) — Correct. File.ReadAllText returns the whole file as a single string; split it into lines with Split.

Complete the ReadAllText call

string text = File.____("hello.txt");

Show answer

string text = File.ReadAllText("hello.txt");

Match each method to its role

ReadAllText

Reads a single string
WriteAllText

Writes a single string
ReadAllLines

Reads an array of lines
Exists

Checks file exists

Next lesson: File.WriteAllText

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