Copy/Read Bytes in Reverse Order-CodePudding

I have this code:

let x:     [u8; 4]  = [0b10111011, 0b00110110, 0b11100010, 0b00010001];
let mut y: [u32; 1] = [0];
    
unsafe {
    std::ptr::copy(x.as_ptr() as *const u32, y.as_mut_ptr(), 1);
}
    
println!("{:b}", y[0]);

The print statement outputs 10001111000100011011010111011, which means y[0] is getting read in the reverse order I need it.

I want y to basically just be [0b10111011_00110110_11100010_00010001].

I know this has to do with endianness, but I don't know how to achieve this. Any help is greatly appreciated.

CodePudding user response：

This is indeed because of your computer storing and reading integers in little endian byteorder, but you specified x in big endian fashion.

Try using u32::from_be_bytes() which avoids the unsafe block and always converts x into the correct u32 representation, whether on a little or big endian machine.

let y = u32::from_be_bytes(x)

Playground