I am surprised by the question: "It's non-standard and it's behavior is
undefined" actually should be enough to avoid such feature.
Actually if a reliable implementation of "#pragma once" would be
possible, that feature would have been included in the C++ standard for
a long time already, wouldn't it?
Ciao
Mathias
Am 10.10.2022 um 11:55 schrieb Volker Hilsheimer via Development:
Hi,
We are using `#pragma once` in a number of examples and tests in the Qt source
tree, but I don’t think we have officially endorsed it in favour of explicit
include guards.
#pragma once is “non-standard but widely supported” [1], with some caveats,
e.g. when there are multiple header files with the same name (which each
compiler then handles differently, as there is no standard).
From what I see, it should in practice be ok to use. But perhaps I’m missing
something. Does anything speak against using ‘#pragma once’ in new files?
Volker
[1] https://en.wikipedia.org/wiki/Pragma_once
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