I'll just add my vote: +1 to supporting the intersection of C99, C11,
C++11, and later standards.
Also +1 to sadness that VLAs don't fall into there. (Though I understand
the reasons why compiler developers might not want to support them.)
--Richard
On 3/11/20 8:34 AM, Jed Brown wrote:
My proposal is for PETSc to support the intersection of C99, C11, C++11,
and any later standards. This (sadly*) excludes VLA.
[*] I don't care about stack allocation, but VLA-pointers are extremely
useful for multi-dimensional array indexing. I'm sad that C11 made that
optional.
Jeff Hammond <[email protected]> writes:
I wonder if it is not more useful to talk in terms of C11 features. Unlike
C99, C11 makes VLAs optional via __STDC_NO_VLA__, so you have a
standardized way of expressing the subset of C11 that is compatible with
C++11. __STDC_NO_ATOMICS__ and __STDC_NO_THREADS__ play a similar role.
Of course, some compilers refuse to use these properly, so PETSc will have
to check compiler support directly rather than trusting macros, but that is
nothing new and Jed (rightly) doesn't trust such compiler macros anyways.
I merely suggest that the macros correspond to an ISO C language definition
for describing the portable subset in a way that C99 cannot.
I don't think the macros are of any utility in defining the
intersection. For example, g++ and clang++ do not set __STDC_NO_VLA__
(and aren't expected to because they aren't C compilers), yet they don't
support the syntax.
double (*a)[n] = (double (*)[n])p;
a[i][j] = 42;
