Rust formatting traits - Display, Debug, hex, binary, and more

The type suffix at the end of a Rust replacement field selects a formatting trait. {} uses Display, {:?} uses Debug, {:x} uses LowerHex, {:b} uses Binary, and the remaining suffixes map to their corresponding std::fmt traits.

Syntax	Trait	Typical use
`{}`	`Display`	user-facing text
`{:?}`	`Debug`	programmer-facing inspection
`{:x?}` / `{:X?}`	`Debug`	Debug with integer fields in lower / upper hex
`{:b}`	`Binary`	base 2 integers
`{:o}`	`Octal`	base 8 integers
`{:x}`	`LowerHex`	lower-case hexadecimal
`{:X}`	`UpperHex`	upper-case hexadecimal
`{:p}`	`Pointer`	pointer address
`{:e}`	`LowerExp`	lower-case exponent notation
`{:E}`	`UpperExp`	upper-case exponent notation

Display is not automatic

Deriving Debug does not implement Display. Display asks the type author to choose one user-facing representation, and Rust intentionally does not provide a derive for that decision.

EXAMPLE: CI-CHECKEDTEST ASSERTED · examples/format-output/src/reference_examples.rs#custom-display

pub struct Coordinate(pub i32, pub i32);

impl fmt::Display for Coordinate {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(formatter, "({}, {})", self.0, self.1)
    }
}

For the complete method signature and a focused explanation of Formatter, write!, and .to_string(), see implement Display for a Rust struct.

Debug vs Display for choosing between user-facing and programmer-facing output
Implement Display for writing a custom {} representation
Number bases and exponent formatting for numeric trait suffixes
Exact format specifier grammar for the order of flags and type suffixes

Open the interactive cheat sheet to compare common specifications by output.