# Using API Notes to Annotate Win32 Header Files **URL:** \ **Category:** Windows\ **Tags:** windows, apinotes\ **Created:** [March 28, 2024, 7:03pm UTC](https://forums.swift.org/t/using-api-notes-to-annotate-win32-header-files/70964 "2024-03-28T19:03:24Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![timsneath](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/timsneath/32/31180_2.png) [@timsneath](https://forums.swift.org/u/timsneath)\ **Post date:** [March 28, 2024, 7:03pm UTC](https://forums.swift.org/t/using-api-notes-to-annotate-win32-header-files/70964/1 "2024-03-28T19:03:24Z")
As a matter of personal interest, I was writing some Win32 code with Swift. The core header support is excellent, thanks I believe to @compnerd and his patient work. But I'd like to work at tweaking some of the annotations. For example, in the following call: ```swift MessageBoxA(nil, "Hello from Swift running on Windows", "Swift Message Box", UINT(MB_ICONINFORMATION)) ``` `MB_ICONINFORMATION` is declared in the C headers as 0x00000040L, which Swift interprets as a signed value. Ideally we'd fix this so that it was interpreted as an unsigned value, so the cast isn't required in the `MessageBoxA` call. My understanding was that we can use [API Notes](https://clang.llvm.org/docs/APINotes.html) to add an annotation that would be picked up at compile time. And indeed, I see `vcruntime.apinotes` in the platform folder alongside the corresponding `.modulemap` file. But when I try and create `winsdk.apinotes` in the same folder as a sidecar to the `.modulemap` file, it doesn't seem to get picked up by the compiler. Is there something else I have to do to get the `.apinotes` file to be recognized by the compiler? ---
**Author:** ![stevapple](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/stevapple/32/31979_2.png) [@stevapple](https://forums.swift.org/u/stevapple)\ **Post date:** [March 28, 2024, 8:09pm UTC](https://forums.swift.org/t/using-api-notes-to-annotate-win32-header-files/70964/2 "2024-03-28T20:09:23Z")
The compiler uses the recognized support files as a VFS overlay to provide seamless integration, without actually copying them (if you noticed the [Traditional Installation steps](https://www.swift.org/install/windows/#support-files)…). So the workaround is simple: copy your `winsdk.apinotes` to where `winsdk.modulemap` actually is: `%UniversalCRTSdkDir%\Include\%UCRTVersion%\um\`. If you don’t have administrator access, or do not want to patch every time Windows SDK is upgraded, you can also put it in `%SDK_ROOT%\usr\lib\swift\apinotes\`, where Apple OSes put their system API notes. ---
**Author:** ![timsneath](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/timsneath/32/31180_2.png) [@timsneath](https://forums.swift.org/u/timsneath)\ **Post date:** [March 28, 2024, 9:15pm UTC](https://forums.swift.org/t/using-api-notes-to-annotate-win32-header-files/70964/3 "2024-03-28T21:15:49Z")
Thanks for the quick reply. I wasn't able to get my API notes working by putting them into `%SDKROOT%\usr\lib\swift\appnotes`, but putting a copy into `%UniversalCRTSdkDir%\Include\%UCRTVersion%\um\` worked a treat. Thanks for sharing the magic incantation! ---
**Author:** ![compnerd](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/compnerd/32/2165_2.png) [@compnerd](https://forums.swift.org/u/compnerd)\ **Post date:** [March 28, 2024, 9:16pm UTC](https://forums.swift.org/t/using-api-notes-to-annotate-win32-header-files/70964/4 "2024-03-28T21:16:10Z")
Adding additional APINotes for the imports is a great idea, but not something that I've gotten around to. I don't think that there is anything that is preventing this work other than time, and so if you have a starting point for this, I think that would be a welcome addition. Perhaps we could even start draining some of the overloads that are in the WinSDK overlay. ---
**Author:** ![stevapple](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/stevapple/32/31979_2.png) [@stevapple](https://forums.swift.org/u/stevapple)\ **Post date:** [March 28, 2024, 11:45pm UTC](https://forums.swift.org/t/using-api-notes-to-annotate-win32-header-files/70964/5 "2024-03-28T23:45:10Z")
> [@timsneath](#): > > appnotes This was an apparent typo:) ---
**Author:** ![timsneath](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/timsneath/32/31180_2.png) [@timsneath](https://forums.swift.org/u/timsneath)\ **Post date:** [March 29, 2024, 1:15am UTC](https://forums.swift.org/t/using-api-notes-to-annotate-win32-header-files/70964/6 "2024-03-29T01:15:04Z")
Ah, just in the forum. I did get the right directory in Windows, though, and it didn't work: ```cmd C:\Users\timsneath\AppData\Local\Programs\Swift\Platforms\5.10.0\Windows.platform\Developer\SDKs\Windows.sdk\usr\lib\swift\apinotes>dir Volume in drive C has no label. Volume Serial Number is 3687-05AC Directory of C:\Users\timsneath\AppData\Local\Programs\Swift\Platforms\5.10.0\Windows.platform\Developer\SDKs\Windows.sdk\usr\lib\swift\apinotes 03/28/2024 01:43 PM . 03/25/2024 12:32 PM .. 03/05/2024 06:20 PM 205 std.apinotes 03/28/2024 02:03 PM 331 winsdk.apinotes 2 File(s) 536 bytes 2 Dir(s) 197,678,280,704 bytes free ```