On Fri, Jun 26, 2015 at 3:03 PM, Francisco Jerez <curroje...@riseup.net> wrote: > Jason Ekstrand <ja...@jlekstrand.net> writes: > >> On Fri, Jun 26, 2015 at 12:08 PM, Francisco Jerez <curroje...@riseup.net> >> wrote: >>> Jason Ekstrand <ja...@jlekstrand.net> writes: >>> >>>> In C, if you partially initialize a structure, the rest of the struct gets >>>> set to 0. C++, however, does not have this rule so GCC throws warnings >>>> whenver NIR_SRC_INIT or NIR_DEST_INIT is used in C++. >>> >>> I don't think that's right, in C++ initializers missing from an >>> aggregate initializer list are also defined to be initialized >>> (value-initialized to be more precise, what would set them to zero in >>> this case just like in C). >> >> Yes, that is correct. I just did a second attempt that, instead, >> defines a static const variable named NIR_SRC_INIT with a partial >> initializer. C++ still gets grumpy and gives me a pile of "missing >> initializer" warnings. >> > That's likely related to the warning flags you have enabled in CXXFLAGS, > not to C++ itself. Maybe you have -Wmissing-field-initializers enabled > for C++ only? > >>>> Since nir.h contains a static inline that uses NIR_SRC_INIT, every C++ >>>> file that includes nir.h complains about this. >>>> >>> I suspect the reason why this causes a warning may be that you're using >>> compound literals? (which are a C99-specific feature and not part of C++) >>> >>>> This patch adds a small static inline function that makes a struct, >>>> memsets it to 0, and returns it. NIR_SRC_INIT and NIR_DEST_INIT are then >>>> wrappers around this function. >>> >>> In C++ you could just call the implicitly defined default constructor >>> for nir_src or nir_dest, like 'nir_src()'. >> >> The implicitly defined default constructor does nothing to POD types, >> so doing so would explicitly *not* perform the desired action of >> zeroing out the data. >> > > Indeed, but 'nir_src()' doesn't only call the implicitly-defined trivial > default constructor, it value-initializes the object (See section 8.5/8 > of the C++14 spec) what for POD types causes all members to be > zero-initialized.
It looks like this greatly depends on your C++ version. If it's C++11 or above, I believe it does get zero-initialized. If it's earlier than C++11, it doesn't. At least that's the way I read this: http://en.cppreference.com/w/cpp/language/value_initialization _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
