unique_ptr can't initialize

Question

I have the following code in a project, and it gives me an error C2059, syntax error "new" that the unique_ptr line is wrong.

#include <memory>

class Nothing {
public:
    Nothing() { };
};
class IWriter
{
    public:
        IWriter() {
        }

        ~IWriter() {
        }
    private:
        std::unique_ptr<Nothing> test(new Nothing());
};

What is happening here?

I tested both `test(new Nothing);` and `test(new Nothing());` — SinisterMJ, Aug 23 '16 at 09:13
You need to initialise it in the constructor, not in the definition. — David, Aug 23 '16 at 09:15
@SinisterMJ As someone who does not use MSVC, I have no idea what ERROR C2059 means. And *"Syntax Error: new"* is not an error message. — Baum mit Augen, Aug 23 '16 at 09:18
Actually it is the precise message: `Error 1 error C2059: syntax error : 'new' d:\tfs\development\IWriter.h` — SinisterMJ, Aug 23 '16 at 09:21
@SinisterMJ If that is true, this is dumb even by MSVC standards. — Baum mit Augen, Aug 23 '16 at 09:49
Yeah, guess why I had no idea what was wrong with my code... — SinisterMJ, Aug 23 '16 at 09:52

songyuanyao · Accepted Answer · 2016-08-23T09:27:36.270

4

You're trying to use default member initializer, but in the wrong way. It must be simply a brace initializer (or equals initializer) (included in the member declaration).

You could use list initialization (since C++11):

std::unique_ptr<Nothing> test{ new Nothing() };

Or member initialization list:

class IWriter
{
    public:
        IWriter() : test(new Nothing) {
        }
        ~IWriter() {
        }
    private:
        std::unique_ptr<Nothing> test;
};

edited Aug 23 '16 at 09:27

answered Aug 23 '16 at 09:15

songyuanyao

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List initialization only works for C++11+ – Simon Kraemer Aug 23 '16 at 09:16
3

`unique_ptr` is a part of C++11 and onwards, and C++11 is 5 years old. How long do we need to keep writing "C++11 onwards"? – Tas Aug 23 '16 at 09:19
Interestingly enough, the list initialization did not work (VS2013), the init in the construction works – SinisterMJ Aug 23 '16 at 09:21

unique_ptr can't initialize

1 Answers1