Pointer in alloc::fmt - Rust
Description: `p` formatting.

Skip to main content

## Pointer

# Trait Pointer

1.36.0 · Source

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

Expand description

`p` formatting.

The `Pointer` trait should format its output as a memory location. This is commonly presented as hexadecimal. For more information on formatters, see the module-level documentation.

Printing of pointers is not a reliable way to discover how Rust programs are implemented. The act of reading an address changes the program itself, and may change how the data is represented in memory, and may affect which optimizations are applied to the code.

The printed pointer values are not guaranteed to be stable nor unique identifiers of objects. Rust allows moving values to different memory locations, and may reuse the same memory locations for different purposes.

There is no guarantee that the printed value can be converted back to a pointer.

## §Examples

Basic usage with `&i32`:

    let x = &42;

    let address = format!("{x:p}"); // this produces something like '0x7f06092ac6d0'

Implementing `Pointer` on a type:

    use std::fmt;

    struct Length(i32);

    impl fmt::Pointer for Length {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            // use `as` to convert to a `*const T`, which implements Pointer, which we can use

            let ptr = self as *const Self;
            fmt::Pointer::fmt(&ptr, f)
        }
    }

    let l = Length(42);

    println!("l is in memory here: {l:p}");

    let l_ptr = format!("{l:018p}");
    assert_eq!(l_ptr.len(), 18);
    assert_eq!(&l_ptr[..2], "0x");

## Required Methods§

1.0.0 · Source

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

Formats the value using the given formatter.

##### §Errors

This function should return `Err` if, and only if, the provided `Formatter` returns `Err`. String formatting is considered an infallible operation; this function only returns a `Result` because writing to the underlying stream might fail and it must provide a way to propagate the fact that an error has occurred back up the stack.

## Dyn Compatibility§

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

## Implementors§

1.4.0 · Source§

### impl<F> Pointer for F
where F: FnPtr,

1.33.0 · Source§

### impl<Ptr> Pointer for Pin<Ptr>
where Ptr: Pointer,

1.0.0 · Source§

### impl<T: ?Sized, A: Allocator> Pointer for Arc<T, A>

1.0.0 · Source§

### impl<T: ?Sized, A: Allocator> Pointer for Box<T, A>

1.0.0 · Source§

### impl<T: ?Sized, A: Allocator> Pointer for Rc<T, A>

Source§

### impl<T: ?Sized, A: Allocator> Pointer for UniqueArc<T, A>

Source§

### impl<T: ?Sized, A: Allocator> Pointer for UniqueRc<T, A>

1.0.0 · Source§

### impl<T> Pointer for &T
where T: ?Sized,

1.0.0 · Source§

### impl<T> Pointer for &mut T
where T: ?Sized,

1.0.0 · Source§

### impl<T> Pointer for *const T
where T: ?Sized,

1.0.0 · Source§

### impl<T> Pointer for *mut T
where T: ?Sized,

1.24.0 · Source§

### impl<T> Pointer for Atomic<*mut T>

Available on `target_has_atomic_load_store=ptr` only.
1.25.0 · Source§

### impl<T> Pointer for NonNull<T>
where T: ?Sized,