Madhurig at 09:58, 9 February 2026

2026-02-09T09:58:02Z

Madhurig at 12:07, 4 December 2025

2025-12-04T12:07:05Z

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Nirmala Venkat: Created page with "{| border="1" |- || '''Visual Cue''' || '''Narration''' |- || '''Slide 1''' || Welcome to the Spoken Tutorial on
2025-10-27T06:41:24Z

Created page with "{| border="1" |- || '''Visual Cue''' || '''Narration''' |- || '''Slide 1''' || <span style="color:#000000;">Welcome to the Spoken Tutorial on </span><span style="color:#000000..."

New page
{| border="1"
|-
|| '''Visual Cue'''
|| '''Narration'''
|-
|| '''Slide 1'''
|| <span style="color:#000000;">Welcome to the Spoken Tutorial on </span><span style="color:#000000;">'''Error handling'''</span><span style="color:#000000;"> in </span><span style="color:#000000;">'''Rust.'''</span>
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
|| <div style="color:#000000;">'''Slide 2'''</div>

<div style="color:#000000;">'''Learning Objectives'''</div>
|| In this tutorial, we will learn about:
* <div style="color:#000000;margin-left:1.27cm;margin-right:0cm;">Recoverable Errors </div>
* <div style="color:#000000;margin-left:1.27cm;margin-right:0cm;">Unrecoverable Errors and</div>
* <div style="color:#000000;margin-left:1.27cm;margin-right:0cm;">Error Propagation Operator</div>

|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.101cm;padding-right:0.191cm;"
|| <div style="color:#000000;">'''Slide 3'''</div>

<div style="color:#000000;">'''System Requirements'''</div>

|| To record this tutorial I’m using the following setup.
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.101cm;padding-right:0.191cm;"
|| <span style="color:#000000;">'''Slide'''</span><span style="color:#000000;"> </span><span style="color:#000000;">'''5'''</span>

<div style="color:#000000;">'''Code Files'''</div>
||
* <div style="color:#000000;margin-left:1.27cm;margin-right:0cm;">The following code file is required to practise this tutorial.</div>
* <div style="color:#000000;margin-left:1.27cm;margin-right:0cm;">This file is provided in the Code Files link of this tutorial page.</div>

|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.101cm;padding-right:0.191cm;"
|| <span style="color:#000000;">'''Slide</span> 6'''

'''Types of Errors'''
|| In Rust, errors are categorized as

<span style="color:#000000;">1. </span><span style="color:#000000;">'''Recoverable Errors'''</span><span style="color:#000000;"> →These are anticipated failures, handled with </span><span style="color:#188038;">Option</span><span style="color:#000000;"> and </span><span style="color:#188038;">Result</span><span style="color:#000000;"> enums</span>

<span style="color:#000000;">2. </span><span style="color:#000000;">'''Unrecoverable Errors'''</span><span style="color:#000000;"> → These are unexpected </span>critical<span style="color:#000000;"> failures. </span>They lead<span style="color:#000000;"> to a </span><span style="color:#000000;">'''panic!'''</span><span style="color:#000000;"> and program termination.</span>
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
|| <span style="color:#000000;">Open </span><span style="color:#000000;">'''Visual'''</span><span style="color:#000000;"> </span><span style="color:#000000;">'''code editor'''</span>
|| <span style="color:#000000;">Open the </span><span style="color:#000000;">'''Visual </span><span style="color:#000000;">S</span><span style="color:#000000;">tudio code editor.'''</span>
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
|| <span style="color:#000000;">In the menu bar, click on </span><span style="color:#000000;">'''Terminal'''</span><span style="color:#000000;"> and select</span><span style="color:#000000;">''' New Terminal'''</span><span style="color:#000000;">.</span>

|| <span style="color:#000000;">In the menu bar, click on </span><span style="color:#000000;">'''Terminal'''</span><span style="color:#000000;"> and select</span><span style="color:#000000;">''' New Terminal'''</span><span style="color:#000000;">.</span>

|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
|| <span style="color:#000000;">'''> cd'''</span><span style="color:#000000;"> </span><span style="color:#000000;">'''Desktop'''</span><span style="color:#000000;">/</span><span style="color:#000000;">'''MyRustProject'''</span>

<span style="color:#000000;">'''>'''</span><span style="color:#000000;"> </span><span style="color:#000000;">'''cargo new errorhandling'''</span>

<div style="color:#000000;">'''In the menu bar, File >> Open folder >> Desktop >> MyRustProject >> errorhandling'''</div>
|| <span style="color:#000000;">Let us go to our working directory </span><span style="color:#000000;">'''MyRustProject'''</span><span style="color:#000000;"> as explained earlier.</span>

<span style="color:#000000;">Type the command </span><span style="color:#000000;">'''cargo new errorhandling '''</span><span style="color:#000000;">and press </span><span style="color:#000000;">'''Enter.'''</span>

<div style="color:#000000;">Open the created project as shown.</div>
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
|| <span style="color:#000000;">Point to the </span><span style="color:#000000;">'''main.rs'''</span><span style="color:#000000;"> file.</span>

|| <span style="background-color:#ffffff;color:#000000;">In the </span><span style="background-color:#ffffff;color:#000000;">'''main.rs '''</span><span style="background-color:#ffffff;color:#000000;">file, copy and paste the code from the Code file.</span>
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
|| <div style="color:#000000;">fn divide(x: f64, y: f64) -> Result<f64, String> {</div>

<div style="color:#000000;">if y == 0.0 {</div>

<div style="color:#000000;">Err(String::from("Cannot divide by zero"))</div>

<div style="color:#000000;">} else {</div>

<div style="color:#000000;">Ok(x / y)</div>

<div style="color:#000000;">}</div>

<div style="color:#000000;">}</div>

<div style="color:#000000;">fn main(){</div>

<div style="color:#000000;">match divide(10.0, 0.0) {</div>

<div style="color:#000000;">Ok(result) => println!("Result: {}", result),</div>

<div style="color:#000000;">Err(e) => println!("Error: {}", e),</div>

<div style="color:#000000;">}</div>

<div style="color:#000000;">}</div>
|| <div style="color:#000000;">This program explains about recoverable errors.</div>

<span style="color:#000000;">Function </span><span style="color:#188038;">divide</span><span style="color:#000000;"> takes two integers as input parameters and returns the division result.</span>

<div style="color:#000000;">What happens if we try to divide an integer by zero without handling it?</div>

<div style="color:#000000;">In Rust, it will cause the program to crash at runtime.</div>

D<span style="color:#000000;">ividing by zero is a known and anticipated failure.</span>

So<span style="color:#000000;"> we</span> <span style="color:#000000;">handle it using the </span><span style="color:#188038;">Result</span><span style="color:#000000;"> enum: </span>

<span style="color:#000000;">If the denominator </span><span style="color:#188038;">y</span><span style="color:#000000;"> is </span><span style="color:#188038;">0</span><span style="color:#000000;">, function returns an </span><span style="color:#188038;">Err</span><span style="color:#000000;"> containing an error message.</span>

<span style="color:#000000;">If the denominator is valid, </span><span style="color:#000000;">function returns the successful division wrapped in </span><span style="color:#188038;">Ok</span><span style="color:#000000;">.</span>

<div style="color:#000000;">Save the program.</div>
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
| style="color:#000000;" |
|| In the terminal, type '''cargo run '''to see the output.

It displays the output as “Cannot divide by zero” as the denominator y is 0 in the code.
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
| style="color:#252525;" |
|| Next let us see an example of an unexpected error.

Clear the code and Copy paste the code from the code file.
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
|| <div style="color:#000000;">fn main() {</div>

<div style="color:#000000;">let v = vec![1, 2, 3];</div>

<div style="color:#000000;">println!("{}", v[99]); // panics: index out of bounds</div>

<div style="color:#000000;">panic!("Something went terribly wrong!");</div>

}

|| <div style="color:#000000;">What happens when the program encounters an unexpected error?</div>

<div style="color:#000000;">That is something we do not anticipate and cannot recover from.</div>

We have declared a vector v with three elements.

In this program, it tries to access the element at index 99, which does '''not exist'''.

After a panic, the program '''stops execution''' — it does not continue to the next line.

<div style="color:#000000;">Save the program.</div>

<div style="color:#252525;">Let us run the program</div>
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
|| <div style="color:#252525;"></div>

<div style="color:#252525;"></div>

<div style="color:#ff0000;"></div>
|| <span style="color:#000000;">In the term</span>inal, type '''cargo run'''

The program prints an error message and the current thread stops.

The panic statement is not executed because the program already panics at the previous line.
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
| style="color:#252525;" |
|| Next we will see about the Error Propagation operator.
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
|| <div style="color:#000000;">Slide:</div>

<div style="color:#000000;">Error Propagation Operator (?)</div>
||
* <div style="color:#000000;margin-left:1.27cm;margin-right:0cm;">Error Propagation Operator (?} automatically returns an error if a function call fails.</div>
* <div style="margin-left:1.27cm;margin-right:0cm;"><span style="color:#000000;">This operator can be only used in functions where it returns </span><span style="color:#000000;">'''option '''</span><span style="color:#000000;">or </span><span style="color:#000000;">'''result enum.'''</span></div>

|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
| style="color:#000000;" |
|| Switch<span style="color:#000000;"> back to the visual code editor.</span>

<div style="color:#000000;">Copy and paste the code from the code file</div>
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
|| <div style="color:#252525;">use std::fs::File;</div>

<div style="color:#252525;">use std::io::{self, Read};</div>

<div style="color:#252525;">fn read_file(filename: &str) -> Result<String, io::Error> {</div>

<div style="color:#252525;">let mut file = File::open(filename)?;// This will return early if File::open fails</div>

<div style="color:#252525;">let mut contents = String::new();</div>

<div style="color:#252525;">file.read_to_string(&mut contents)?;// This will return early if read_to_string fails</div>

<div style="color:#252525;">Ok(contents)</div>

<div style="color:#252525;">}</div>

<div style="color:#252525;">fn main() {</div>

<div style="color:#252525;">match read_file("hello.txt") {</div>

<div style="color:#252525;">Ok(content) => println!("File content: {}", content),</div>

<div style="color:#252525;">Err(e) => println!("Error reading file: {}", e),</div>

<div style="color:#252525;">}</div>

<div style="color:#252525;">}</div>

|| <div style="color:#000000;"></div>

In this example we try to read the file contents and return the '''Result enum.'''

<span style="color:#252525;">The </span><span style="color:#252525;">'''read_file'''</span><span style="color:#252525;"> takes a filename which is of type string slice.</span>

<span style="color:#252525;">It returns a </span><span style="color:#252525;">'''Result enum'''</span><span style="color:#252525;"> with </span><span style="color:#252525;">'''Ok'''</span><span style="color:#252525;"> </span><span style="color:#252525;">'''type'''</span><span style="color:#252525;"> </span><span style="color:#252525;">as</span><span style="color:#252525;"> String and </span><span style="color:#252525;">'''Err'''</span><span style="color:#252525;"> </span><span style="color:#252525;">'''type'''</span><span style="color:#252525;"> as</span><span style="color:#252525;"> input output error.</span>

<span style="color:#252525;">At the line </span><span style="color:#252525;">'''File::open(filename)?,'''</span><span style="color:#252525;"> it attempts to open the file, with the ? operator</span>

<div style="color:#252525;">If successful, it continues execution with the file handle.</div>

<span style="color:#252525;">If it fail</span><span style="color:#252525;">s</span><span style="color:#252525;">, it returns the error from the function.</span>

<span style="color:#252525;">Next we initialised a mutable variable called </span><span style="color:#252525;">'''contents'''</span><span style="color:#252525;">.</span>

<span style="color:#252525;">It is of the type </span><span style="color:#252525;">'''String'''</span><span style="color:#252525;"> object.</span>

<span style="color:#252525;">'''read_to_string'''</span><span style="color:#252525;"> reads all the bytes of the file till </span><span style="color:#252525;">e</span><span style="color:#252525;">nd and </span><span style="color:#252525;">appends them to </span><span style="color:#252525;">'''contents.'''</span>

<span style="color:#252525;">The ? Operator returns the error </span><span style="color:#252525;">immediately if</span><span style="color:#252525;"> it fails.</span>

<span style="color:#252525;">If everything succeeds, it </span><span style="color:#252525;">returns</span><span style="color:#252525;"> the file content.</span>

<span style="color:#252525;">In main function, we use </span><span style="color:#252525;">'''match'''</span><span style="color:#252525;"> arms to handle </span><span style="color:#252525;">results</span><span style="color:#252525;"> returned </span><span style="color:#252525;">by </span><span style="color:#252525;">'''read_file'''</span><span style="color:#252525;"> function.</span>

<div style="color:#000000;">Save the program.</div>
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
| style="color:#000000;" |
|| <span style="color:#000000;">In the terminal, type </span><span style="color:#000000;">'''cargo run'''</span>

We can see the error message “Error reading file”.

This shows that the file '''hello.txt''' is not available.
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
| style="color:#000000;" |
|| <div style="color:#000000;">This brings us to the end of this tutorial.</div>

<div style="color:#000000;">Let us summarize. </div>
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
|| <div style="color:#000000;">'''Slide 8'''</div>

|| As an assignment, do the following

1. Create '''hello.txt''' file and with the text “Welcome to Rust tutorials”

2. Save the file in the errorhandling folder

3. Run the <span style="color:#000000;">Error Propagation Operator program </span>and check<span style="color:#000000;"> the output</span>

|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
| style="color:#000000;" | '''Slide 9 Thank You'''
| style="color:#000000;" | Thanks for joining.
|-
|}
<div style="margin-left:-1.588cm;margin-right:-1.429cm;"></div>

@@ Line 136: / Line 136: @@
 We have declared a vector '''v''' with three elements.
-In this program, it tries to access the element at index 99, which does  not exist.
+In this program, it tries to access the element at index 99, which does not exist.
 After a panic, the program '''stops execution''', it does not continue to the next line.
@@ Line 236: / Line 236: @@
 |-
 || '''Slide 8'''
-|| As an assignment, do the following
+|| As an assignment, do the following:
-. Create '''hello.txt''' file and with the text “Welcome to Rust tutorials”
+. Create '''hello.txt''' file and with the text “Welcome to Rust tutorials”.
-. Save the file in the error handling folder
+. Save the file in the error handling folder.
-. Run the Error Propagation Operator program and check the output
+. Run the Error Propagation Operator program and check the output.
 |-

Rust-Programming-Language/C2/Error-Handling/English - Revision history

Madhurig at 09:58, 9 February 2026

Madhurig at 12:07, 4 December 2025