https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91808
Bug ID: 91808
Summary: Static definition rejected after extern declaration in
anonymous namespace
Product: gcc
Version: 9.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: andrey.vihrov at gmail dot com
Target Milestone: ---
Consider the following C++11 sample:
namespace
{
extern int x;
static int x = 0;
}
Compiling this with "gcc -c test.cpp" gives
test.cpp:4:16: error: '{anonymous}::x' was declared 'extern' and later 'static'
[-fpermissive]
4 | static int x = 0;
| ^
test.cpp:3:16: note: previous declaration of '{anonymous}::x'
3 | extern int x;
| ^
According to [1], point 3.5.4, the "extern int x;" declaration has the same
linkage as its enclosing namespace, which is anonymous and thus has internal
linkage. According to point 3.1.2, this declaration is not a definition.
According to point 3.5.3, the "static int x = 0;" declaration has internal
linkage. It is also the first definition for the internal "int {anonymous}::x"
variable. Overall, this declaration doesn't conflict with the previous one.
Note: Clang (starting with version 6) and MSVC accept the code.
[1] http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3690.pdf
