How to find a CLSID in rust for windows?

Question

I'm using rust for windows to use the win32 API.
However, I need to initialize com library to use some windows APIs, but I cannot find some classes ID (CLSID), to create an instance.
I need to find the Speech ISpVoice CLSID to use in my instance creation.
CLSID_SpVoice is the CLSID.
Also, I cannot find some macros like "FAILED", and "SUCCEEDED".
If anyone can direct me, that would be appreciated!
Also, if there's any error in my code, please highlight it me.
Code:

    use windows::Win32::System::Com::{CoInitializeEx, CoCreateInstance};
use windows::Win32::System::{Com, Ole};
use windows::core::{ HRESULT, Error };
use windows::Win32::Media::Speech::ISpVoice;

fn main() {
    let speaker: ISpVoice;
    unsafe {
        if CoInitializeEx(std::ptr::null(), Com::COINIT_MULTITHREADED) ==Result::Ok(()) {
            let hr: HRESULT = CoCreateInstance(, punkouter, dwclscontext)
        }
    }
}

If anything is unclear, please let me know!

Answer 1

The windows crate declares the SpVoice constant which is the value of the CLSID_SpVoice class ID. As you have discovered, that's the CLSID you want to pass into CoCreateInstance.

The latter returns a windows::core::Result<T>, which models the same semantics as C code using the SUCCEEDED and FAILED macros would. You can either match on the Ok or Err variants manually, or use the ? operator for convenient error propagation:

use std::ptr;

use windows::{
    core::Result,
    Win32::{
        Media::Speech::{ISpVoice, SpVoice},
        System::Com::{CoCreateInstance, CoInitializeEx, CLSCTX_ALL, COINIT_APARTMENTTHREADED},
    },
};

fn main() -> Result<()> {
    unsafe { CoInitializeEx(ptr::null(), COINIT_APARTMENTTHREADED) }?;
    let _speaker: ISpVoice = unsafe { CoCreateInstance(&SpVoice, None, CLSCTX_ALL) }?;

    Ok(())
}

In case you need a CLSID that's not available through the windows crate, you can always construct a GUID constant using either from_values or from_u128:

const CLSID_SpVoice: GUID = GUID::from_u128(0x96749377_3391_11d2_9ee3_00c04f797396);

Note that the value is exactly the value you were given in a comment. Your assessment that C++ and Rust were any different with respect to COM is unfounded. They are indeed the same thing, just with different syntax.

Answer 2

I found the solution.
I'll let my answer for anyone may encounter this problem:
Instead of providing the Class ID of the ISpVoice, I referenced the SpVoice struct to the CoCreateInstance method then it returns the SpVoice struct.
As following:

let speaker: ISpVoice = CoCreateInstance(&SpVoice, None, CLSCTX_ALL)?;

This method will work with any CoCreateInstance.
However, I'm still stuck with the two macros: "FAILED", and "SUCCEEDED".
If anyone know, please let me know also.