Document somewhere that enums can be either c_int or c_uint

[saschanaz]

Input C/C++ Header

enum TestEnum {
  FOO,
  BAR
};

Bindgen Invocation

$ bindgen input.h

Actual Results

On Windows:

/* automatically generated by rust-bindgen 0.56.0 */

pub const TestEnum_FOO: TestEnum = 0;
pub const TestEnum_BAR: TestEnum = 1;
pub type TestEnum = ::std::os::raw::c_int;

On Ubuntu:

/* automatically generated by rust-bindgen 0.56.0 */

pub const TestEnum_FOO: TestEnum = 0;
pub const TestEnum_BAR: TestEnum = 1;
pub type TestEnum = ::std::os::raw::c_uint;

Expected Results

This should be documented somewhere. All I found is this comment: #1096 (comment)

Bindgen uses whatever enum type comes from clang, so if it's a u32, clang is picking a u32 type for it.

[emilio]

A more precise definition is that bindgen will use std::underlying_type_t<Enum>. But yeah, adding docs for this would be great.

[Lokathor]

can we have an option to just always make a c_int on all platforms, because the signedness only matters to Rust and C doesn't care?

[ghost]

Resurrecting this thread because we just stumbled upon the same issue. In our case we have something like the following:

pub const my_enum_VALUE_0: my_enum = 0;
pub const my_enum_VALUE_1: my_enum = 1;
...
pub type my_enum = u32;

I believe the problem here is that the enumeration constants should always be int, as specified by the C standard, rather than my_enum. The type of my_enum itself can be whatever clang spits out. In any case, it would be nice to have an option to control this as @Lokathor suggested.

[FSMaxB]

Just stumbled over this as well. For reference: https://stackoverflow.com/a/366033/1717115

Basically the C standard specifies that an enum value always needs to be representable by int, although the compiler can choose different types for the actual representation.