b formatting.

The Binary trait should format its output as a number in binary.

For primitive signed integers (i8 to i128, and isize), negative values are formatted as the two’s complement representation.

The alternate flag, #, adds a 0b in front of the output.

For more information on formatters, see the module-level documentation.

Examples

Basic usage with [i32]:

let x = 42; // 42 is '101010' in binary

assert_eq!(format!("{x:b}"), "101010");
assert_eq!(format!("{x:#b}"), "0b101010");

assert_eq!(format!("{:b}", -16), "11111111111111111111111111110000");

Implementing Binary on a type:

use std::fmt;

struct Length(i32);

impl fmt::Binary for Length {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let val = self.0;

        fmt::Binary::fmt(&val, f) // delegate to i32's implementation
    }
}

let l = Length(107);

assert_eq!(format!("l as binary is: {l:b}"), "l as binary is: 1101011");

assert_eq!(
    // Note that the `0b` prefix added by `#` is included in the total width, so we
    // need to add two to correctly display all 32 bits.
    format!("l as binary is: {l:#034b}"),
    "l as binary is: 0b00000000000000000000000001101011"
);