As Rust does not support bitfields, Bindgen generates a struct for each with the following characteristics
<bitfield>
set_<bitfield>
new_bitfield_{1, 2, ...}
with a parameter for each bitfield contained within the opaque physical field.For this discussion, we will use the following C type definitions and functions.
typedef struct { unsigned int a: 1; unsigned int b: 1; unsigned int c: 2; } StructWithBitfields; // Create a default bitfield StructWithBitfields create_bitfield(); // Print a bitfield void print_bitfield(StructWithBitfields bfield);
Bindgen creates a set of field getters and setters for interacting with the bitset. For example,
let mut bfield = unsafe { create_bitfield() }; bfield.set_a(1); println!("a set to {}", bfield.a()); bfield.set_b(1); println!("b set to {}", bfield.b()); bfield.set_c(3); println!("c set to {}", bfield.c()); unsafe { print_bitfield(bfield) };
will print out
a set to 1 b set to 1 c set to 3 StructWithBitfields: a:1, b:1, c:3
Overflowing a bitfield will result in the same behavior as in C/C++: the bitfield will be set to 0.
let mut bfield = unsafe { create_bitfield() }; bfield.set_a(1); bfield.set_b(1); bfield.set_c(12); println!("c set to {} due to overflow", bfield.c()); unsafe { print_bitfield(bfield) };
will print out
c set to 0 due to overflow StructWithBitfields: a:1, b:1, c:0
To create a new bitfield in Rust, use the bitfield allocation unit constructor.
Note: This requires the Builder‘s derive_default to be set to true, otherwise the necessary Default functions won’t be generated.
let bfield = StructWithBitfields{ _bitfield_1: StructWithBitfields::new_bitfield_1(0,0,0), ..Default::default() }; unsafe { print_bitfield(bfield) };
This will print out
StructWithBitfields: a:0, b:0, c:0