Printing a path in Rust

Question

How could I print a path in Rust?

I tried the following in order to print the current working directory:

use std::os;

fn main() {
    let p = os::getcwd();
    println!("{}", p);
}

But rustc returns with the following error:

[wei2912@localhost rust-basics]$ rustc ls.rs 
ls.rs:5:17: 5:18 error: failed to find an implementation of trait core::fmt::Show for std::path::posix::Path
ls.rs:5     println!("{}", p);
                           ^
note: in expansion of format_args!
<std macros>:2:23: 2:77 note: expansion site
<std macros>:1:1: 3:2 note: in expansion of println!
ls.rs:5:2: 5:20 note: expansion site

Answer 1

As you discovered, the "correct" way to print a Path is via the .display method, which returns a type that implements Display.

There is a reason Path does not implement Display itself: formatting a path to a string is a lossy operation. Not all operating systems store paths compatible with UTF-8 and the formatting routines are implicitly all dealing with UTF-8 data only.

As an example, on my Linux system a single byte with value 255 is a perfectly valid filename, but this is not a valid byte in UTF-8. If you try to print that Path to a string, you have to handle the invalid data somehow: .display will replace invalid UTF-8 byte sequences with the replacement character U+FFFD, but this operation cannot be reversed.

In summary, Paths should rarely be handled as if they were strings, and so they don't implement Display to encourage that.

Answer 2

The following will print out the full path:

println!("{}", p.display());

Refer to Path::display for more details.

Answer 3

As a related tangent, I've written a library for when you "just want it in UTF-8" stfu8.

This uses escape characters (i.e. \x00) to format any nearly-UTF-8 sequence the way a developer might expect.