[cfe-dev] Compound literals in C++: why rvalue?

[Enea Zaffanella]

We recently saw from clang sources that compound literals are classified
as lvalues in C, but not in C++ (when used as extensions).

Is this intentional and, if so, can someone provide a pointer to the
relevant documentation? (As far as we can tell, they are classified as
lvalues for both C/C++ in recent versions of gcc).

While passing, here is a testcase (using r147790) showing that a crash
is obtained when specifying -W[no-]address-of-temporary:

$ cat bug.cc
int (*pa)[1] = &(int[]) { 1 };


$ clang++ -c bug.cc
bug.cc:1:16: error: taking the address of a temporary object of type
'int [1]'
      [-Waddress-of-temporary]
int (*pa)[1] = &(int[]) { 1 };
               ^~~~~~~~~~~~~~
1 error generated.


$ clang++ -Waddress-of-temporary -c bug.cc
bug.cc:1:16: warning: taking the address of a temporary object of type
'int [1]'
      [-Waddress-of-temporary]
int (*pa)[1] = &(int[]) { 1 };
               ^~~~~~~~~~~~~~
clang: <path>/tools/clang/lib/AST/ExprConstant.cpp:2479: bool
EvaluateLValue(const clang::Expr*, <unnamed>::LValue&,
<unnamed>::EvalInfo&): Assertion `(E->isGLValue() ||
E->getType()->isFunctionType() || E->getType()->isVoidType() ||
isa<CXXTemporaryObjectExpr>(E)) && "can't evaluate expression as an
lvalue"' failed.
[...]


Enea.