- std::hexfloat - 2 Updates
| "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com>: May 19 11:21PM +0200 On 19.05.2019 21:10, David Brown wrote: > (And that's not just theory - faffing around with casting pointer types > as you did does not work on anything but the most limited of compilers, > and usually only with optimisations disabled.) C supports type punning via unions. C++ does not. C++ does not, in the strictest interpretation of the formal, support general type punning except by way of `memcpy`. I disagree with that interpretation: it's totally impractical, so IMO it can't be the /intent/. However, the GCC folks have generally adopted the most silly, impractically rigid literal interpretations of the formal rules, so I would absolutely not be surprised if they assume the aforementioned one too. I don't know of any way to tell the C++ compiler that look, these two pointers are of different types but access the same bytes in memory. And the thing about UB, even purely formal UB, is that the compiler can /assume/ that it will not happen, e.g. it can assume that the code dereferencing that 2nd pointer and accessing the pointee, will never be executed. Then the compiler can optimize it away. That's what g++ does in a number of cases, so perhaps also in this one, if one's unlucky. Cheers!, - Alf |
| Sal LO <gegefffffff@gmail.com>: May 19 02:57PM -0700 https://youtu.be/O909xMoMfKk |
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