Why bindgen interpret wchar_t type as ::std::os::raw::c_int?

[Al-Rozhkov]

This is a question.

I have compiled dynamic C library, a header file for it and a documentation. I successfully built bindings with bindgen. I got pub type wchar_t = ::std::os::raw::c_int; in my bindings.rs. But looks like C function must accept wchar_t as string.

Input C Header

#define SETTING_KEY L"OfdChannel"

DTOX_SHARED_EXPORT void DTOX_SHARED_CCA ffi_set_single_setting(lib_handle handle, const wchar_t *key, const wchar_t *value);

bindings.rs

pub const SETTING_KEY: &'static [u8; 11usize] = b"OfdChannel\0";
pub type wchar_t = ::std::os::raw::c_int;

extern "C" {
    pub fn ffi_set_single_setting(
        handle: libfptr_handle,
        key: *const wchar_t,
        value: *const wchar_t,
    );
}

I'm struggling to create safe wrapper around this functions because key const has type [u8] but the function expects i32 (c_int) as argument.

Here is my wrapper:

pub fn set_single_setting(&self) {
  let raw_key: *const _ = &SETTING_KEY;
  let value = 2;
  let raw_value: *const i32 = &value;
  unsafe {
    ffi_set_single_setting(self.handle, raw_key, raw_value);
    ffi_apply_single_settings(self.handle);
  }
}

It doesn't compile: raw_key expected to be i32, found &[u8; 11].

What am I doing wrong? Any help would be appreciated.

[emilio]

You're not doing anything wrong, as far as I can tell. The bug is not in the function signature, but in the constant definition, that should ideally be a wide char array.

I took a look, and cexpr doesn't give any hint that we could use to distinguish. So this is a problem in there.

I filed #1745, closing as a dupe of that.

[Al-Rozhkov]

@emilio thank you!

You posted link to exact this issue. Should be jethrogb/rust-cexpr#25 (Allow to distinguish wide strings from regular strings) I guess.

[emilio]

Err, whoops, indeed :)

[emilio]

In the meantime, though ugly (and assuming the key won't change), you can do something like:

const KEY: [wchar_t; 11] = [b'O' as wchar_t, ..., b'\0' as wchar_t];
unsafe {
    ffi_set_single_setting(self.handle, KEY.as_ptr(), ...);
}

Or if you're in control of the C headers you can do something like:

extern const wchar_t BINDGEN_SETTING_KEY[] = SETTING_KEY;

And you should be able to use the BINDGEN_ version and it should have the right type.