Small C++ query

Hi folks,

I’m confused by the following code snippet:

#include
void foo(int *x) { std::unique_ptr(x); }

both clang and gcc warn that this redefines x, but I don’t understand why this
is a declaration of x. I guess I would have expected a temporary unique_ptr that gets destructed immediately or an error. How come this actually defines a variable called x?

To give some background about where this came up, a user wanted to do
C++> std::unique_ptr(x);
in my Clang-based interactive C++ REPL. Behind the scenes this gets transformed into the function above and then I try to insert a return statement on the last statement in the body to automatically grab the result. This works well in most cases but failed here because Clang thinks this is a variable declaration, so I’d like to understand why this is happening.

Keno

Hi folks,

I’m confused by the following code snippet:

#include
void foo(int *x) { std::unique_ptr(x); }

both clang and gcc warn that this redefines x, but I don’t understand why this
is a declaration of x. I guess I would have expected a temporary unique_ptr that gets destructed immediately or an error. How come this actually defines a variable called x?

The C and C++ grammars allow redundant parenthesis around names being declared (technically, declarators).
If you wish to construct a temporary, use the brace notation, aka uniform initialization syntax.

Thank you everyone.

I knew about this difficulty in parsing, but did not realize it applied to this situation. Makes sense. Thanks!