# Trait core::fmt::UpperHex

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``````pub trait UpperHex {
// Required method
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}``````
Expand description

`X` formatting.

The `UpperHex` trait should format its output as a number in hexadecimal, with `A` through `F` in upper case.

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

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

## §Examples

Basic usage with `i32`:

``````let y = 42; // 42 is '2A' in hex

assert_eq!(format!("{y:X}"), "2A");
assert_eq!(format!("{y:#X}"), "0x2A");

assert_eq!(format!("{:X}", -16), "FFFFFFF0");``````
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Implementing `UpperHex` on a type:

``````use std::fmt;

struct Length(i32);

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

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

let l = Length(i32::MAX);

assert_eq!(format!("l as hex is: {l:X}"), "l as hex is: 7FFFFFFF");

assert_eq!(format!("l as hex is: {l:#010X}"), "l as hex is: 0x7FFFFFFF");``````
Run

## Required Methods§

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#### fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

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