Panic!

When something goes terribly wrong in Rust there might occur a panic.

Setup

✅ Go to intro/panic directory.

✅ Open the prepared project skeleton in intro/panic.

✅ Open the docs for this project with the following command:

cargo doc --open

intro/panic/examples/panic.rs contains the solution. You can run it with the following command:

cargo run --example panic

Exercise

✅ In main.rs add a panic! somewhere, e.g. after our println

✅ Run the code

cargo run

We see where the panic occurred, and we even see a backtrace!

While in this example things are obvious, this will come in handy in more complex code.

✅ Now try running the code compiled with release profile.

cargo run --release

Now things are less pretty:

!! A panic occured in 'examples\panic.rs', at line 15, column 5:
This is a panic

Backtrace:

0x42000100
0x42000100 - _start_rust
    at ??:??

We still see where the panic occurred, but the backtrace is less helpful now.

That is because the compiler omitted debug information and optimized the code, you might have noticed the difference in the size of the flashed binary.

Generally you want to use release always. To get a more helpful backtrace when using the release profile you can add this to your .cargo/config.toml

[profile.release]
debug = true

This will include debug information in the ELF file - but that won't get flashed to the target so it's something you can and should always use.

If you are reusing this project for other exercises, be sure to remove the line causing the explicit panic.

Simulation

This project is available for simulation through two methods:

• Wokwi projects:
  • Exercise: Currently not available
  • Solution
• Wokwi files are also present in the project folder to simulate it with Wokwi VS Code extension:
  1. Press F1, select Wokwi: Select Config File and choose intro/panic/wokwi.toml
     • Edit the wokwi.toml file to select between exercise and solution simulation
  2. Build you project
  3. Press F1 again and select Wokwi: Start Simulator