ImportC and #pragma pack

[Walter Bright]

On 9/28/2021 12:52 PM, Guillaume Piolat wrote:
> On Tuesday, 28 September 2021 at 17:32:26 UTC, Walter Bright wrote:
>> On 9/28/2021 5:50 AM, Guillaume Piolat wrote:
>>> The conundrum with ImportC is that it seems to me you have to build with the 
>>> right cstdlib headers if you intend to use this or that backend.
>>
>> Not sure what that means.
> 
> I mean that the ImportC preprocessor needs libc headers, and those SHOULD be the 
> same libc that the code will be linked against.

Just like for any C code, the .h files must match the library binaries.


> 1. Suppose you use ImportC right now, using the TinyCC with its own cstlib 
> headers, for the purpose of preprocessing C code in order to give to ImportC.
> 
> The preprocessed C code has the following `dirent` struct:
> https://github.com/TinyCC/tinycc/blob/82b0af74501bf46b16bc2a4a9bd54239aa7b7127/win32/include/dirent.h#L25 
> 
> 
> 2. You link with the libc that comes with DMD or LDC, so the clang or msvc or 
> Digital Mars one. They contains another `dirent` struct definition
> 
> 3. At runtime, the C stdlib has its own understanding of what is the `dirent` 
> struct. A memory corruption ensues right after calling readdir() and reading the 
> result.

Of course that will fail, just like it will fail if you compile code with 
TinyCC's stdlib and link with clang's stdlib.