Make the Linux and Windows backends compile as C++#1848
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Building libusb as C++ (useful for analysis tools and compiler flags that only run in C++ mode) needs explicit casts plus a few C/C++ keyword differences. PR #1782 makes the common code and the Darwin backend build as C++; this change is the orthogonal companion covering the Linux and Windows pieces it does not touch. - libusbi.h: use the GCC __atomic builtins instead of <stdatomic.h> when compiling as C++ with GCC. g++ cannot parse <stdatomic.h> in C++ mode before C++23 (the _Atomic keyword); previously only the Haiku path worked around this. C and clang builds are unchanged. - os/threads_posix.c: map C11 _Thread_local to thread_local under C++. - os/linux_usbfs.c: explicit casts on void*-returning allocations and usbi_get_*_priv() accessors, cast an int transfer status to its enum, and reorder the usbi_os_backend initializer to declaration order (C++ requires designated initializers in order). - os/windows_common.{c,h}, os/windows_winusb.{c,h}, os/windows_usbdk.c, os/events_windows.c: explicit casts on void*-returning allocations and accessors; compare GUIDs with memcmp (IsEqualGUID takes references in C++); cast an enum to uint8_t to avoid a narrowing warning under /WX. All casts are no-ops in C and preserve behavior. Verified locally that #1782 + this change builds cleanly as C++ with g++ (Linux) and MSVC (Windows). Refs: #1782 Assisted-by: claude-code:claude-opus-4-8
Youw
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Jun 6, 2026
Youw
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Jun 6, 2026
Youw
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Jun 6, 2026
- libusbi.h: reword the atomics comment to keep the original Haiku
context and note the GCC __atomic builtins are used for any GCC C++
build, so no separate C++23 path is needed.
- os/threads_posix.c: simplify the _Thread_local/thread_local comment.
- os/windows_winusb.{c,h}: fix the WinUsb_ReadIsochPipeAsap_t typedef -
its first argument was PWINUSB_ISOCH_BUFFER_HANDLE but the WinUSB API
(and WriteIsochPipeAsap) take WINUSB_ISOCH_BUFFER_HANDLE by value.
Correcting it drops the void* cast the C++ build otherwise needed.
Refs: #1782
Assisted-by: claude-code:claude-opus-4-8
Add usbi_guid_equal() in windows_common.h, which calls IsEqualGUID and hides its C-vs-C++ signature difference (pointers in C, const GUID& references in C++) behind #ifdef __cplusplus, and use it in windows_winusb.c instead of the earlier raw memcmp. Keeps the intent clear while still compiling as both C and C++. Refs: #1782 Assisted-by: claude-code:claude-opus-4-8
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Summary
Building libusb as C++ (useful for static-analysis tools and compiler flags that only run in C++ mode) needs a set of explicit casts plus a couple of C-vs-C++ keyword differences. #1782 makes the common code + the Darwin backend build as C++; this PR is the orthogonal companion covering the Linux and Windows pieces #1782 doesn't touch. It's independent of #1782 (no overlapping changes) and can land before or after it.
What it fixes
libusbi.h(atomics) — g++ can't include<stdatomic.h>in C++ mode before C++23 (the_Atomickeyword); this was by far the biggest blocker on Linux (>400 cascading errors). Use the GCC__atomicbuiltins for any GCC C++ build (previously only the Haiku path did). C and clang builds are unchanged.os/threads_posix.c— map C11_Thread_localtothread_localunder__cplusplus(g++ rejects_Thread_localin C++).os/linux_usbfs.c— explicit casts onvoid*allocations andusbi_get_*_priv()accessors; cast aninttransfer status to its enum; reorder theusbi_os_backendinitializer to the struct's declaration order (C++ requires designated initializers in order).windows_common.{c,h},windows_winusb.{c,h},windows_usbdk.c,events_windows.c) — explicit casts onvoid*allocations/accessors; compare GUIDs withmemcmp(IsEqualGUIDtakes references in C++); one enum→uint8_tnarrowing cast for/WX.All casts are no-ops in C and preserve behavior.
Verification (reproduced locally on Windows + WSL)
-std=c++20): the.sobuilds cleanly./TP,CompileAs=CompileAsCpp): the DLL builds cleanly (0 warnings under/WX).The C++-build CI proposed in #1845 exercises exactly this.
Refs: #1782
Assisted-by: claude-code:claude-opus-4-8