Decimal number to hexadecimal string

Question

Does Rust have a set of functions that make converting a decimal integer to a hexadecimal string easy? I have no trouble converting a string to an integer, but I can't seem to figure out the opposite. Currently what I have does not work (and may be a bit of an abomination)

Editor's note - this code predates Rust 1.0 and no longer compiles.

pub fn dec_to_hex_str(num: uint) -> String {
    let mut result_string = String::from_str("");
    let mut i = num;
    while i / 16 > 0 {
        result_string.push_str(String::from_char(1, from_digit(i / 16, 16).unwrap()).as_slice());
        i = i / 16;
    }
    result_string.push_str(String::from_char(1, from_digit(255 - i * 16, 16).unwrap()).as_slice());

    result_string
}

Am I on the right track, or am I overthinking this whole thing?

Incidentally, string.push_str(String::from_char(1, char).as_slice()) is impressively inefficient; to do something like that, string.push_char(char) is what you should do. — Chris Morgan
– Chris Morgan, Commented Jul 29, 2014 at 3:46
@ChrisMorgan thanks for the pointer, I'm very new to rust coming from c++ and know some of the concepts i'm using are bad. — Syntactic Fructose
– Syntactic Fructose, Commented Jul 29, 2014 at 3:50

Shepmaster · Accepted Answer · 2017-03-07 13:45:59Z

104

You’re overthinking the whole thing.

assert_eq!(format!("{:x}", 42), "2a");
assert_eq!(format!("{:X}", 42), "2A");

That’s from std::fmt::LowerHex and std::fmt::UpperHex, respectively. See also a search of the documentation for "hex".

edited Mar 7, 2017 at 13:45

Shepmaster

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answered Jul 29, 2014 at 2:43

Chris Morgan

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1 Comment

Chris Morgan Over a year ago

@10cls: as_slice was just for getting the &str out of the String so you could compare it with a string slice. assert_eq! has changed now so that you don’t even need & or &* as in &*format!(…).

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