Jason Ekstrand <ja...@jlekstrand.net> writes: > 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
Not really, it will get zero-initialized back to C++98. AFAICT what the article is trying to say is that in C++98 what is now referred to as value-initialization used to be called default-initialization in the spec, but still it had the effect of zero-initializing the structure.
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