Gcc hidden Members in struct

Currently, I am working with an embedded device.

I am creating my own "register representation" to learn the process in the C Language.

I do this via structs placed at given locations:

struct myIo {
   u32 flagA : 1;
   u32 fieldB : 7;
   u32 reserved : 24;
   u32 regB;
};

struct __attribute__((section("sec"))) myIo MyIo;

This works just fine and all, but I wonder how I could remove the

reserved

fields without compromising the padding/alignment enforced by the hardware.

My question is:

How could I design a struct with "hidden" fields, that won't show up when I access the struct.

In essence:

MyStruct.reserved = val;

or

val = MyStruct.reserved;

should throw a compiler error and typing

MyIo.

should not bring up "Auto-Complete" options in Eclipse CDT C/C++.

I am using Arm Cross GCC and Eclipse CDT C/C++.

I am good with C-Standard compliant solutions, compiler pragma solutions and preprocessor solutions.

You can create an unnamed bitfield:

struct myIo {
   u32 flagA : 1;
   u32 fieldB : 7;
   u32 : 24;
   u32 regB;
};

Such constructs are allowed as per section 6.7.2.1p12 of the C standard regarding "Structure and union specifiers":

> A bit-field declaration with no declarator, but only a colon and a
> width, indicates an unnamed bit-field. ¹²⁶⁾ As a special
> case, a bit-field structure member with a width of 0 indicates that no
> further bit-field is to be packed into the unit in which the previous
> bit- field, if any, was placed.
>
> ---
>
> 126 ) An unnamed bit-field structure member is useful for padding to
> conform to externally imposed layouts.

Note that a zero-sized bitfield will also work in this case, but only because no other bitfields follow it.