[Cython] Compilation failes if a class member is named "INFINITY"

[Stefan Behnel]

Michael schrieb am 05.02.2015 um 09:52:
> Am 31.01.2015 um 19:48 schrieb Matthew Brett:
>> On Fri, Jan 30, 2015 at 1:49 AM, Michael wrote:
>>> if I try to compile the following minimal example:
>>>
>>> cdef class Test:
>>>
>>>     cdef readonly int INFINITY
>>>
>>> cython does not complain but gcc refuses with an error message:
>>> In file included from /usr/include/math.h:38:0,
>>>                  from /usr/include/python2.7/pyport.h:325,
>>>                  from /usr/include/python2.7/Python.h:58,
>>>                  from testinf.c:16:
>>> testinf.c:433:7: error: field '__builtin_inff' declared as a function
>>>    int INFINITY;
>>>        ^
>>> testinf.c: In function '__pyx_pf_7testinf_4Test_8INFINITY___get__':
>>> testinf.c:569:50: error: expected identifier before '(' token
>>>    __pyx_t_1 = __Pyx_PyInt_From_int(__pyx_v_self->INFINITY); if
>>> (unlikely(!__pyx_t_1)) {__pyx_filename = __pyx_f[0]; __pyx_lineno = 10;
>>> __pyx_clineno = __LINE__; goto __pyx_L1_error;}
>>>                                                   ^
>>> Apparently the name "INFINITY" is handled wrongly; any other variable
>>> name seems to be fine.
>>
>> Maybe you hit the INFINITY gcc macro?
>>
>> http://www.gnu.org/software/libc/manual/html_node/Infinity-and-NaN.html
> 
> Yes, that's probably the explanation. So should Cython do anything about
> the problem, i.e. raise an exception if struct members are named like a
> macro?

Cython cannot know about everything that the C compiler (or its
preprocessor) will eventually see in its flat namespace. So, no, Cython
can't generally solve this problem for you.


> I don't know about the Cython internals, but I wonder why the name not
> altered in the c file:
>  struct __pyx_obj_7testinf_Test {
>   PyObject_HEAD
>   int INFINITY;
> };
> I would have expected something like "int __pyx_member_INFINITY"?

Python extension types are just structs at the C level, and struct member
names cannot be mangled. Plus, when types are external or public (or even
just redeclared somewhere else by someone else), foreign code may depend on
struct fields of extension types as well. Builtin types are an example.

Stefan