dtolnay/cxx

Adding windows pointer/integer data types

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#254 opened on Aug 15, 2020

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Description

I have been trying to access a 3rd-party win32 API using cxx. One of the first things I am coming across is that the library contains extensive use of windows-specific type aliases like DWORD, WPARAM, LPARAM, HINSTANCE etc. most of which are equivalent to an unsigned integer of some size (u32 in case of 32-bit windows). Now obviously, since cxx is unaware of this, I am unable to pass or return these by value.

If I try to use u32 inside of the extern "C" block, I get errors like:

lib.rs.cc(10): error C2440: 'initializing': cannot convert from 'DWORD (__thiscall MyClass::* )(DWORD)' to 'uint32_t (__thiscall MyClass:
:* )(uint32_t)'
lib.rs.cc(10): note: Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
exit code: 2

Is there any workaround to this to make cxx "aware" of that these types are interchangeable with unsigned integers? I believe most of these are defined in minwindef.h in the windows SDK.

Contributor guide

Tech stack
rustcpp
Domain
developer experienceapi
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
basic RustWindows SDK knowledge
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Investigate how cxx currently handles C++ type aliases and consider adding a way to declare them as equivalent to Rust integer types. Look into the Windows SDK header `minwindef.h` for definitions of DWORD, WPARAM, etc. The maintainer's response or existing comments may provide hints on the preferred approach.