Reading text files in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the basic method to read all text from a file in C#?

Use File.ReadAllText(path) to read the entire content of a text file as a single string.

beginner

How can you read a text file line by line in C#?

Use File.ReadLines(path) or File.ReadAllLines(path) to get each line as a string, allowing you to process the file line by line.

beginner

What namespace must you include to work with file reading in C#?

Include using System.IO; to access file reading methods like File.ReadAllText and File.ReadLines.

intermediate

What is the difference between File.ReadAllText and File.ReadAllLines?

File.ReadAllText reads the whole file into one string.<br><br>File.ReadAllLines reads the file into a string array, each element is one line.

intermediate

Why should you handle exceptions when reading files in C#?

Because files might not exist, be locked, or have permission issues. Handling exceptions like FileNotFoundException or IOException prevents crashes and allows graceful error handling.

Which method reads the entire content of a text file into a single string?

A File.ReadAllText

B File.ReadLines

C File.ReadAllLines

D File.WriteAllText

File.ReadAllText reads the whole file content as one string.

Which namespace do you need to include to read files in C#?

A System.Text

B System.IO

C System.Net

D System.Collections

System.IO contains classes for file input and output.

What does File.ReadLines return?

A A byte array of the file content

B An array of strings, each representing a line

C A single string with all file content

D An IEnumerable&lt;string&gt; to read lines lazily

File.ReadLines returns an IEnumerable<string> that reads lines one by one, which is memory efficient.

Which exception should you catch when a file is missing?

A FileNotFoundException

B ArgumentNullException

C IndexOutOfRangeException

D FormatException

FileNotFoundException is thrown when the file path does not exist.

What is a good practice when reading files?

A Ignore exceptions to keep code simple

B Always read files without checking if they exist

C Handle exceptions to avoid program crashes

D Use <code>Console.ReadLine()</code> to read files

Handling exceptions like IOException helps your program handle errors gracefully.

Explain how to read a text file line by line in C# and why it might be better than reading the whole file at once.

Think about memory usage and processing big files.

Describe the exceptions you should handle when reading a file and why handling them is important.

Consider what can go wrong when accessing files.