Rust, how to slice into a byte array as if it were a float array?-CodePudding

I have some byte data stred in a &[u8] I know for a fact the data contained in the slice is float data. I want to do the equivalent of auto float_ptr = (float*)char_ptr;

I tried:

let data_silce = &body[buffer_offset..(buffer_offset buffer_length)] as &[f32];

But you are not allowed to execute this kind of casting in rust.

CodePudding user response：

You will need to use unsafe Rust to interpret one type of data as if it is another.

You can do:

let bytes = &body[buffer_offset..(buffer_offset   buffer_length)];

let len = bytes.len();
let ptr = bytes.as_ptr() as *const f32;
let floats: &[f32] = unsafe { std::slice::from_raw_parts(ptr, len / 4)};

Note that this is Undefined Behaviour if any of these are true:

the size of the original slice is not a multiple of 4 bytes
the alignment of the slice is not a multiple of 4 bytes

All sequences of 4 bytes are valid f32s but, for types without that property, to avoid UB you also need to make sure that all values are valid.

CodePudding user response：

You can use std::mem::transmute. Mind the length of the slice.

    let a = [1u8, 2, 3, 4];
    let b: &[f32] = unsafe {
        &std::mem::transmute::<&[u8], &[f32]>(&a)[0..a.len() / 4]
    };

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