# Missing C definitions in Swift interface **URL:** \ **Category:** Using Swift\ **Tags:** c, c-interop, interoperability\ **Created:** [April 5, 2025, 3:04pm UTC](https://forums.swift.org/t/missing-c-definitions-in-swift-interface/79113 "2025-04-05T15:04:33Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![LouChiSoft](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/louchisoft/32/40376_2.png) [@LouChiSoft](https://forums.swift.org/u/LouChiSoft)\ **Post date:** [April 5, 2025, 3:04pm UTC](https://forums.swift.org/t/missing-c-definitions-in-swift-interface/79113/1 "2025-04-05T15:04:33Z")
Hi, Swift newbie here. I previously asked for help with wrapping a C library with Swift (specifically SDL). Now I have ran into another issue, while mapping the C API to Swift I have noticed that in the `.swiftinterface` file that is generated by the Swift compiler/package manager several definitions are missing. It's not like the entire header is missing and the file isn't being parsed. Most of the header is mapped and only some of the `#defines` are missing. SDL\_video.h snippet ```swift /** * The flags on a window. * * These cover a lot of true/false, or on/off, window state. Some of it is * immutable after being set through SDL_CreateWindow(), some of it can be * changed on existing windows by the app, and some of it might be altered by * the user or system outside of the app's control. * * \since This datatype is available since SDL 3.2.0. * * \sa SDL_GetWindowFlags */ typedef Uint64 SDL_WindowFlags; #define SDL_WINDOW_FULLSCREEN SDL_UINT64_C(0x0000000000000001) #define SDL_WINDOW_OPENGL SDL_UINT64_C(0x0000000000000002) #define SDL_WINDOW_OCCLUDED SDL_UINT64_C(0x0000000000000004) #define SDL_WINDOW_HIDDEN SDL_UINT64_C(0x0000000000000008) #define SDL_WINDOW_BORDERLESS SDL_UINT64_C(0x0000000000000010) #define SDL_WINDOW_RESIZABLE SDL_UINT64_C(0x0000000000000020) #define SDL_WINDOW_MINIMIZED SDL_UINT64_C(0x0000000000000040) #define SDL_WINDOW_MAXIMIZED SDL_UINT64_C(0x0000000000000080) #define SDL_WINDOW_MOUSE_GRABBED SDL_UINT64_C(0x0000000000000100) #define SDL_WINDOW_INPUT_FOCUS SDL_UINT64_C(0x0000000000000200) #define SDL_WINDOW_MOUSE_FOCUS SDL_UINT64_C(0x0000000000000400) #define SDL_WINDOW_EXTERNAL SDL_UINT64_C(0x0000000000000800) #define SDL_WINDOW_MODAL SDL_UINT64_C(0x0000000000001000) #define SDL_WINDOW_HIGH_PIXEL_DENSITY SDL_UINT64_C(0x0000000000002000) #define SDL_WINDOW_MOUSE_CAPTURE SDL_UINT64_C(0x0000000000004000) #define SDL_WINDOW_MOUSE_RELATIVE_MODE SDL_UINT64_C(0x0000000000008000) #define SDL_WINDOW_ALWAYS_ON_TOP SDL_UINT64_C(0x0000000000010000) #define SDL_WINDOW_UTILITY SDL_UINT64_C(0x0000000000020000) #define SDL_WINDOW_TOOLTIP SDL_UINT64_C(0x0000000000040000) #define SDL_WINDOW_POPUP_MENU SDL_UINT64_C(0x0000000000080000) #define SDL_WINDOW_KEYBOARD_GRABBED SDL_UINT64_C(0x0000000000100000) #define SDL_WINDOW_VULKAN SDL_UINT64_C(0x0000000010000000) #define SDL_WINDOW_METAL SDL_UINT64_C(0x0000000020000000) #define SDL_WINDOW_TRANSPARENT SDL_UINT64_C(0x0000000040000000) #define SDL_WINDOW_NOT_FOCUSABLE SDL_UINT64_C(0x0000000080000000) /** * A magic value used with SDL_WINDOWPOS_UNDEFINED. * * Generally this macro isn't used directly, but rather through * SDL_WINDOWPOS_UNDEFINED or SDL_WINDOWPOS_UNDEFINED_DISPLAY. * * \since This macro is available since SDL 3.2.0. */ #define SDL_WINDOWPOS_UNDEFINED_MASK 0x1FFF0000u ``` Corresponding section in the `.swiftinterface` file ```swift /** * The flags on a window. * * These cover a lot of true/false, or on/off, window state. Some of it is * immutable after being set through SDL_CreateWindow(), some of it can be * changed on existing windows by the app, and some of it might be altered by * the user or system outside of the app's control. * * \since This datatype is available since SDL 3.2.0. * * \sa SDL_GetWindowFlags */ public typealias SDL_WindowFlags = Uint64 public var SDL_WINDOWPOS_UNDEFINED_MASK: UInt32 { get } ``` As you can see it is missing all of the `SDL_WINDOW_*` definitions as well as the comment for `SDL_WINDOWPOS_UNDEFINED_MASK` which as far as I can tell should also have been copied over. There are other missing definitions too, but these ones are pretty critical to map correctly. Anyone have any idea what's going on? ---
**Author:** ![LouChiSoft](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/louchisoft/32/40376_2.png) [@LouChiSoft](https://forums.swift.org/u/LouChiSoft)\ **Post date:** [April 6, 2025, 6:30am UTC](https://forums.swift.org/t/missing-c-definitions-in-swift-interface/79113/2 "2025-04-06T06:30:25Z")
Doing some extra digging, I have found that the missing definitions are any Macro or definition that uses a macro e.g. `#define SDL_WINDOW_FULLSCREEN SDL_UINT64_C(0x0000000000000001)` uses the `SDL_UINT64_C` macro and is skipped. Only the `#defines` that explicitly define a concrete value are included. Is this an intended limitation of the C wrapping system? ---
**Author:** ![j-f1](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/j-f1/32/12287_2.png) [@j-f1](https://forums.swift.org/u/j-f1)\ **Post date:** [April 6, 2025, 2:45pm UTC](https://forums.swift.org/t/missing-c-definitions-in-swift-interface/79113/3 "2025-04-06T14:45:39Z")
Yes, the clang importer only accepts a subset of C syntax in macro definitions when creating Swift symbols. The way I most often see code work around this is by declaring a C function that returns the value of the macro, then calling that from Swift. ---
**Author:** ![kateinoigakukun](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/kateinoigakukun/32/16706_2.png) [@kateinoigakukun](https://forums.swift.org/u/kateinoigakukun)\ **Post date:** [April 7, 2025, 2:05am UTC](https://forums.swift.org/t/missing-c-definitions-in-swift-interface/79113/4 "2025-04-07T02:05:58Z")
Yes, this is a known limitation of ClangImporter. Here are related tickets: - [[SR-4096] Generated interface of #define XXX (\) isn't created · Issue #46679 · swiftlang/swift · GitHub](https://github.com/swiftlang/swift/issues/46679) - [[SR-485] C macros of the form ((long long)-1) should be imported · Issue #43102 · swiftlang/swift · GitHub](https://github.com/swiftlang/swift/issues/43102) ---
**Author:** ![LouChiSoft](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/louchisoft/32/40376_2.png) [@LouChiSoft](https://forums.swift.org/u/LouChiSoft)\ **Post date:** [April 7, 2025, 10:02am UTC](https://forums.swift.org/t/missing-c-definitions-in-swift-interface/79113/5 "2025-04-07T10:02:01Z")
Damn, that's a shame. I could understand the more complex macros that use things like stringify not being imported because the context isn't clear. But most of the missing macros in SDL3 that I have come across have all been `#define NAME (some constant express)` when you expand them. Hopefully this is something that gets improved upon so I don't have to maintain additional C code that might end up out of date with the core SDL3 library. ---
**Author:** ![saulpalv](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/saulpalv/32/42373_2.png) [@saulpalv](https://forums.swift.org/u/saulpalv)\ **Post date:** [May 29, 2025, 5:52pm UTC](https://forums.swift.org/t/missing-c-definitions-in-swift-interface/79113/6 "2025-05-29T17:52:59Z")
Rust C import has also uses clang and has a workaround with `--clang-macro-fallback`, [see gh thread](https://github.com/rust-lang/rust-bindgen/issues/3098)