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# Using the Bitfield Types Generated by Bindgen
## Bitfield Strategy Overview
As Rust does not support bitfields, Bindgen generates a struct for each with the following characteristics
* Immutable getter functions for each bitfield named ```<bitfield>```
* Setter functions for each contiguous block of bitfields named ```set_<bitfield>```
* Far each contiguous block of bitfields, Bindgen emits an opaque physical field that contains one or more logical bitfields
* A static constructor ```new_bitfield_{1, 2, ...}``` with a parameter for each bitfield contained within the opaque physical field.
## Bitfield examples
For this discussion, we will use the following C type definitions and functions.
```c
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,
```rust,ignore
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
```text
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.
```rust,ignore
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
```text
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.
```rust,ignore
let bfield = StructWithBitfields{
_bitfield_1: StructWithBitfields::new_bitfield_1(0,0,0),
..Default::default()
};
unsafe { print_bitfield(bfield) };
```
This will print out
```text
StructWithBitfields: a:0, b:0, c:0
```
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