abort and unwind

The previous section illustrates the error handling mechanism panic.

Different code paths can be conditionally compiled based on the panic setting.

The current values available are abort and unwind.

Implementation mechanism of panic

In Rust, there are two ways to implement panic: unwind and abort

1. In the unwind mode, when a panic occurs, the function calls will be exited layer by layer. During the process, the local variables in the current stack can be destructed normally.
2. The abort method will directly exit the entire program when a panic occurs.
3. Generally speaking, by default, the compiler uses the unwind mode.

How to make it yourself:

rustc -C panic=unwind test.rs
rustc -C panic=abort test.rs

abort

~~~admonish tip title="cfg!(panic='abort'): Building on the prior lemonade example, we explicitly use the panic strategy to exercise different lines of code. " collapsible=true 
```rust,editable,mdbook-runnable

fn drink(beverage: &str) {
   // You shouldn't drink too much sugary beverages.
    if beverage == "lemonade" {
        if cfg!(panic="abort"){ println!("This is not your party. Run!!!!");}
        else{ println!("Spit it out!!!!");}
    }
    else{ println!("Some refreshing {} is all I need.", beverage); }
}

fn main() {
    drink("water");
    drink("lemonade");
}
```
~~~

unwind

#[cfg(panic = "unwind")]
fn ah(){ println!("Spit it out!!!!");}

#[cfg(not(panic="unwind"))]
fn ah(){ println!("This is not your party. Run!!!!");}

fn drink(beverage: &str){
    if beverage == "lemonade"{ ah();}
    else{println!("Some refreshing {} is all I need.", beverage);}
}

fn main() {
    drink("water");
    drink("lemonade");
}

rustc  lemonade.rs -C panic=abort

cfg! or #cfg

#[cfg(panic = "unwind")]
fn ah(){ println!("Spit it out!!!!");}

cfg!(panic="abort"){ println!("This is not your party. Run!!!!");}