# Windows.h clobbers public regulated data types generated code

**URL:** <https://forum.opencyphal.org/t/windows-h-clobbers-public-regulated-data-types-generated-code/1994>\
**Category:** Nunavut\
**Created:** [October 5, 2023, 5:44pm UTC](https://forum.opencyphal.org/t/windows-h-clobbers-public-regulated-data-types-generated-code/1994 "2023-10-05T17:44:56Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![willeccles](https://forum.opencyphal.org/user_avatar/forum.opencyphal.org/willeccles/32/1400_2.png) [@willeccles](https://forum.opencyphal.org/u/willeccles)\
**Post date:** [October 5, 2023, 5:44pm UTC](https://forum.opencyphal.org/t/windows-h-clobbers-public-regulated-data-types-generated-code/1994/1 "2023-10-05T17:44:56Z")

</div>

While working on a project using `nnvg`, I discovered that my code built perfectly with GCC, but would fail to build with MSVC. The error was in the generated header file for `uavcan.si.unit.pressure.Scalar.1.0`. Given the following struct declaration:

```c
typedef struct
{
    /// saturated float32 pascal
    float pascal; /* Line 86 */
} uavcan_si_unit_pressure_Scalar_1_0;

```

MSVC was reporting a syntax error at the declaration of `float pascal` (followed by about a million more errors):

```auto
....\out\uavcan\si\unit\pressure\Scalar_1_0.h(86): error C2059: syntax error: ';'

```

I was quite puzzled by this for several hours. After much digging, I found that some of my code was including Windows.h before including all the generated headers. It turns out that minwindef.h, which is included by Windows.h, contains the following:

```c
#if (!defined(_MAC)) && ((_MSC_VER >= 800) || defined(_STDCALL_SUPPORTED))
#define pascal __stdcall
#else
#define pascal
#endif

```

Thus, after the preprocessor stage, the declaration was changed from `float pascal;` to `float __stdcall;`, which does indeed result in invalid syntax at the semicolon. Naturally, this was trivially fixed by adding `#undef pascal` after including Windows.h. However, since this include was in code which I cannot modify, I instead resorted to copying the default C templates for `nnvg` and adding `#undef pascal` to base.j2.

As I could find almost no evidence online that this `pascal` macro existed in the first place, and furthermore, I could find no evidence that anyone had run into this with nunavut before, I thought it best to make this post for future readers who may encounter the same headache I did.

**My environment** :

- Windows 10
- Visual Studio 2022 (Professional)
- MSVC version 19.34.31937.0
- Windows 10 SDK version 10.0.22621.0

---

<div class="post-metadata">

**Author:** ![scottdixon](https://forum.opencyphal.org/user_avatar/forum.opencyphal.org/scottdixon/32/39_2.png) [@scottdixon](https://forum.opencyphal.org/u/scottdixon)\
**Post date:** [October 10, 2023, 5:36pm UTC](https://forum.opencyphal.org/t/windows-h-clobbers-public-regulated-data-types-generated-code/1994/2 "2023-10-10T17:36:05Z")

</div>

Nice find. I’ve opened [`pascal` is a keyword on Windows · Issue #318 · OpenCyphal/nunavut · GitHub](https://github.com/OpenCyphal/nunavut/issues/318) to track a fix for this.