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

Research direction
Explore how cxx currently handles C++ types and identify where Windows specific types like DWORD, WPARAM, LPARAM are defined. Investigate how to extend the type mapping to allow these types to be treated as unsigned integers. Look at existing type alias mechanisms in cxx and consider adding Windows type aliases to the supported list.
Tech stack
rustcpp
Domain
api
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.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
RustC++Windows API
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40