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c++multithreading
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Reputation: 31

C++: request for thread member for class, cannot be access

I'm trying to write a class include a public thread object, and finally I want to access this thread ouside the class, but there are some errors, why?

The class defined as:

class scoped_thread {
public:
    std::thread t;
    explicit scoped_thread(std::thread t_) : t(std::move(t_)) {
        if (!t.joinable()) 
            throw std::logic_error("No thread");

    }

    ~scoped_thread() {
        // t.join();
    }

    scoped_thread(scoped_thread const &) = delete;
    scoped_thread & operator = (scoped_thread const &) = delete;
};

and I'm try to access thread member:

scoped_thread th(std::thread(f));
th.t.join();

At last, the error is:

error: request for member 't' in 'th', which is of non-class type 'scoped_thread(std::thread)'

Upvotes: 1

Views: 53

Answers (2)

Ray Hamel
Ray Hamel

Reputation: 1309

You've run into the most vexing parse. C++ thinks you've declared a function named th instead of an object. In recent versions of C++, to correct the issue you can use curly braces instead of parentheses.

scoped_thread th{std::thread{f}}; // compiles as expected

Upvotes: 3

Igor Tandetnik
Igor Tandetnik

Reputation: 52621

scoped_thread th(std::thread(f)); is a declaration of a function named th, returning scoped_thread and taking std::thread as a parameter. It's not a declaration of an object of type scoped_thread. Naturally, the function doesn't have members, named t or otherwise.

See also: most vexing parse.

Upvotes: 3

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