https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99625
Bug ID: 99625
Summary: GCC does not detect narrowing in aggregate
initialization
Product: gcc
Version: 10.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: dangelog at gmail dot com
Target Milestone: ---
Testcase:
extern long double l;
struct S {
S(int) {}
};
S s[] = { l };
This is supposed to be ill-formed because of narrowing. GCC does not reject the
code, nor it warns (as it usually does for narrowing).
The relevant rule is in [dcl.init.aggr]:
https://eel.is/c++draft/dcl.init.aggr#4.2.sentence-2
> Otherwise, the element is copy-initialized from the corresponding
> initializer-clause or is initialized with the brace-or-equal-initializer of
> the corresponding designated-initializer-clause.
> If that initializer is of the form assignment-expression or =
> assignment-expression and a narrowing conversion ([dcl.init.list]) is
> required to convert the expression, the program is ill-formed.
That rule has been changed in C++20 with designated initializers, but the same
one was also there for C++17 and before, e.g.
https://timsong-cpp.github.io/cppwp/n4659/dcl.init.aggr#3
For comparison, Clang accepts with no warnings, but MSVC warns about narrowing.
