Hello, Is there was to put endianness to get bytes from Struct like so

for both big and little endian, you should be writing the struct field by field
Don’t rely on the as *const _ technique as the compiler can rearrange fields, even beyond reordering and alignment - the Rust compiler optimises memory layout much more than a C or C++ compiler would
Take a look at the byteorder crate, which has helper functions for writing fields in little or big endian format