Rust for C-Programmers

2.11 Error Handling

2.11.1 Result and Option Types

Rust does not use exceptions for error handling. Instead, it uses the Result and Option types.

fn divide(a: f64, b: f64) -> Result<f64, String> {
    if b == 0.0 {
        Err(String::from("Cannot divide by zero"))
    } else {
        Ok(a / b)
    }
}

fn main() {
    match divide(4.0, 2.0) {
        Ok(result) => println!("Result is {}", result),
        Err(e) => println!("Error: {}", e),
    }
}

2.11.2 Comparison with C

C typically handles errors using return codes and errno.

#include <stdio.h>
#include <errno.h>
#include <math.h>

int divide(double a, double b, double *result) {
    if (b == 0.0) {
        errno = EDOM; // Domain error
        return -1;
    } else {
        *result = a / b;
        return 0;
    }
}

int main() {
    double res;
    if (divide(4.0, 0.0, &res) != 0) {
        perror("Error");
    } else {
        printf("Result is %f\n", res);
    }
    return 0;
}