https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92576
Bug ID: 92576
Summary: Definition of variable template without initializer is
treated as declaration
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Keywords: accepts-invalid
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
GCC accepts this as a declaration followed by a definition, but it should be
two definitions (with the first being ill-formed):
template<typename T> constexpr bool var;
template<typename T> constexpr bool var = false;
Clang says:
inline.cc:1:37: error: default initialization of an object of const type 'const
bool'
template<typename T> constexpr bool var;
^
= false
inline.cc:2:37: error: redefinition of 'var'
template<typename T> constexpr bool var = false;
^
inline.cc:1:37: note: previous definition is here
template<typename T> constexpr bool var;
^
2 errors generated.
EDG says:
"inline.cc", line 1: error: missing initializer for constexpr variable
template<typename T> constexpr bool var;
^
"inline.cc", line 2: error: variable template "var" has already been defined
template<typename T> constexpr bool var = false;
^
"inline.cc", line 2: error: "constexpr" is not valid here
template<typename T> constexpr bool var = false;
^
3 errors detected in the compilation of "inline.cc".
MSVC says:
example.cpp
<source>(1): error C2737: 'var': 'constexpr' object must be initialized
<source>(2): error C2086: 'const bool var': redefinition
<source>(1): note: see declaration of 'var'
Compiler returned: 2
I think 'extern' is needed to stop the first line being a definition:
template<typename T> extern constexpr bool var;
template<typename T> constexpr bool var = false;
G++ correctly rejects it for a non-template inline variable:
constexpr bool var;
constexpr bool var = false;
inline.cc:1:16: error: uninitialized const ‘var’ [-fpermissive]
constexpr bool var;
^~~
inline.cc:2:16: error: redefinition of ‘constexpr const bool var’
constexpr bool var = false;
^~~
inline.cc:1:16: note: ‘constexpr const bool var’ previously declared here
constexpr bool var;
^~~
