On Mon, 7 Feb 2022 15:29:39 +0100
Victor Stinner <[email protected]> wrote:
> On Mon, Feb 7, 2022 at 2:26 PM Victor Stinner <[email protected]> wrote:
> > CPython is also affected by these issues, but the benefits of PEP 674
> > (alone) are too indirect, so I chose to avoid mentioning CPython
> > issues directly, to avoid confusion.
>
> A concrete example of problem caused by exposing structures in the C
> API (unrelated to PEP 674). It's a tricky problem...
>
> typedef struct {
> PyObject_VAR_HEAD
> Py_hash_t ob_shash;
> char ob_sval[1];
> } PyBytesObject;
>
> The "char ob_sval[1];" syntax used to declare an array is an undefined
> behavior if the array is longer in memory. On a bytes object of 4
> bytes, accessing ob_sval[3] works, but is an undefined behavior.
>
> => see https://bugs.python.org/issue40120 for details
>
> The problem can be solved by using "char ob_sval[];" syntax, but we
> cannot use this syntax in the public C header, since it causes
> compiler errors if the header is built with a C++ compiler (not to
> build Python itself, but build a C++ extension using the Python C
> API). Removing the structure from the public C API would solve the C++
> issue.
You could also have something like:
typedef struct {
PyObject_VAR_HEAD
Py_hash_t ob_shash;
#ifdef __cpluscplus
char ob_sval[1];
#else
char ob_sval[];
#endif
} PyBytesObject;
Regards
Antoine.
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