examples/rust-by-example-formatted-print/src/main.rs
fn main() {
// In general, the `{}` will be automatically replaced with any
// arguments. These will be stringified.
let days = 31;
let name = "Foo";
println!("{days} days {name}");
// Positional arguments can be used. Specifying an integer inside `{}`
// determines which additional argument will be replaced. Arguments start
// at 0 immediately after the format string.
println!("{0}, this is {1}. {1}, this is {0}", "Alice", "Bob");
let a = 5;
let b = 7;
println!("{a} + {b} = {c}", c = a + b);
// As can named arguments.
println!("{subject} {verb} {object}",
object="the lazy dog",
subject="the quick brown fox",
verb="jumps over");
// Different formatting can be invoked by specifying the format character
// after a `:`.
println!("Base 10: {}", 69420); // 69420
println!("Base 2 (binary): {:b}", 69420); // 10000111100101100
println!("Base 8 (octal): {:o}", 69420); // 207454
println!("Base 16 (hexadecimal): {:x}", 69420); // 10f2c
// You can right-justify text with a specified width. This will
// output " 1". (Four white spaces and a "1", for a total width of 5.)
println!("<{number}>", number=1);
println!("<{number:>5}>", number=1);
println!("<{number:<5}>", number=1);
println!("<{number:^5}>", number=1);
// // You can pad numbers with extra zeroes,
println!("{number:0>5}", number=1); // 00001
// // and left-adjust by flipping the sign. This will output "10000".
println!("{number:0<5}", number=1); // 10000
// You can use named arguments in the format specifier by appending a `$`.
let width = 4;
println!("{number:0>width$}", number=1);
// Rust even checks to make sure the correct number of arguments are used.
println!("My name is {0}, {1} {0}", "Bond", "James");
// FIXME ^ Add the missing argument: "James"
// Only types that implement fmt::Display can be formatted with `{}`. User-
// defined types do not implement fmt::Display by default.
#[allow(dead_code)] // disable `dead_code` which warn against unused module
struct Structure(i32);
// This will not compile because `Structure` does not implement
// fmt::Display.
// println!("This struct `{}` won't print...", Structure(3));
// TODO ^ Try uncommenting this line
// For Rust 1.58 and above, you can directly capture the argument from a
// surrounding variable. Just like the above, this will output
// " 1", 4 white spaces and a "1".
let number: f64 = 1.0;
let width: usize = 5;
println!("{number:>width$}");
}
