Porting a packed C++ struct with bitfields

[barvazos]

Hi,
Thank you for your help!
I am trying to read a packed struct from file created in a CPP app.
This is the original struct:
`struct HeaderStruct
{
uint16_t _t : 3;

uint16_t _p : 1;

uint16_t _l : 12;

uint16_t _s : 2;

uint16_t _q : 14;

} attribute((packed));
`

This is how I tried to implement it using your crate:
`
#[derive(PackedStruct)]
#[packed_struct(bit_numbering="msb0")]
struct HeaderStruct {
#[packed_field(bits="0..=2")]
_t: Integer<u16, packed_bits::Bits::<3>>,

#[packed_field(bits="3..=3")]
_p: Integer<u16, packed_bits::Bits::<1>>,

#[packed_field(bits="4..=15", endian="msb")]
_l: Integer<u16, packed_bits::Bits::<12>>,

#[packed_field(bits="16..=17")]
_s: Integer<u16, packed_bits::Bits::<2>>,

#[packed_field(bits="18..=31", endian="msb")]
_q: Integer<u16, packed_bits::Bits::<14>>,

}`

in main what I tried to do is:
fn main() { ... let mut hdr_buffer = [0u8; 4]; file.read(&mut hdr_buffer).unwrap(); let hdr = HeaderStruct::unpack(&hdr_buffer); }

I get the following error:

error[E0599]: the method pack exists for reference &packed_struct::types::MsbInteger<_, _, packed_struct::types::Integer<u8, packed_struct::types::bits::Bits<12_usize>>>, but its trait bounds were not satisfied
--> src/main.rs:21:10
|
21 | #[derive(PackedStruct)]
| ^^^^^^^^^^^^ method cannot be called on &packed_struct::types::MsbInteger<_, _, packed_struct::types::Integer<u8, packed_struct::types::bits::Bits<12_usize>>> due to unsatisfied trait bounds
|
::: /Users/amitaihandler/.cargo/registry/src/github.com-1ecc6299db9ec823/packed_struct-0.10.1/src/types_num.rs:14:1
|
14 | pub struct Integer<T, B> {
| ------------------------ doesn't satisfy _: SizedInteger<_, _>
...
571 | pub struct MsbInteger<T, B, I>(I, PhantomData, PhantomData);
| ------------------------------------------------------------------ doesn't satisfy _: packed_struct::PackedStruct
|
= note: the following trait bounds were not satisfied:
packed_struct::types::Integer<u8, packed_struct::types::bits::Bits<12_usize>>: SizedInteger<_, _>
which is required by packed_struct::types::MsbInteger<_, _, packed_struct::types::Integer<u8, packed_struct::types::bits::Bits<12_usize>>>: packed_struct::PackedStruct
= note: this error originates in the derive macro PackedStruct (in Nightly builds, run with -Z macro-backtrace for more info)

If I understand correctly you cannot unpack a 2 bit into a 16 bit? How can I keep the struct size whilst reading from file? Sorry if this question seems trivial... thank you for any help you can offer