How does one round a floating point number to a specified number of digits?

Question

How does one round a f64 floating point number in Rust to a specified number of digits?

Answer 1

To add to @huon's great answer, if you want to round a floating point number for display purposes, but you don't know the precision at compile time, you can use the precision formatting syntax as follows:

fn main() {
    let precision = 3;
    let x = 12.34567;
    println!("{:.1$}", x, precision); // prints 12.346 and works with `format!` as well
}

The documentation of std::fmt has more examples on the syntax.