On Thu, 21 Jan 2021, Michael Matz wrote:
You can't declare a struct in the declaration part of the for stmt
(6.8.5p3), only objects of auto and register class.
Hmmm. I think the spec is somewhat ambiguous here.
The specific wording is:
The declaration part of a for statement shall only declare identifiers
for objects having storage class auto or register
Does that mean that:
1. all objects which have identifiers declared for them must have
storage class auto or register
2. all identifiers which are declared must be for objects, and those
objects must have storage class auto or register
FWIW both gcc and clang seem to nominally follow interpretation 2 (they're
not consistent about it). But I think there's a case to be made for
interpretation 1. In particular, it seems somewhat sensible to disallow
something like 'for (extern int x;;)'. But disallowing
for (int x = sizeof(struct foo { int m; });;)
while allowing
int x = sizeof(struct foo { int m; });
seems arbitrary and inconsistent.
(Maybe I'll write a paper for WG14. Make them disambiguate!)
-E
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