On 2022-10-11 22:04, Thiago Macieira wrote:
...
// This macro can be used to calculate member offsets for types with a non
standard layout. // It uses the fact that offsetof() is allowed to support
those types since C++17 as an optional // feature. All our compilers do
support this, but some issue a warning, so we wrap the offsetof() // call
in a macro that disables the compiler warning.
And we had a lengthy discussion on whether it was acceptable to use offsetof
and such like in our public headers. It was touch and go for a while.
But as the comment you quoted says, offsetof() on non-stdlayout types is
recognised by the standard explicitly. It's not required, but the standard
says it's permitted.
The pragma, on the other hand...
Same example. The comment on Q_OFFSETOF hints that C++17 seems to allow for
optional implementations to go beyond what the standard specifies. Why is
not standardized then? I think the same could be said about this pragma.
What it does is conceptually very simple, and if it only can hurt on very
corner cases, then it's a matter of weighting the tradeoffs.
... can't be standardised because the standard can't come up with a meaningful
description of what a file is. It's unable to add text that explains the
behaviour compilers should have, because it doesn't even have the concept of
files and filesystem where the compiler is running.
Sometime in the far future when Qt requires c++20 things might improve:
we could use std::source_location::filename
(https://en.cppreference.com/w/cpp/utility/source_location/file_name )
||
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