CODEWITHSUNDEEP
c++visual-c++c++11visual-studio-2012move-semantics
Jack Willson
Jack Willson

Reputation: 2104

Move constructor issue

I have the following class:

class Student
{
private:
    std::string firstName;
    std::string lastName;
public:
    Student():firstName(""), lastName("") 
    { 
    }

    Student(const std::string &first, const std::string &last)
        :firstName(first), lastName(last) 
    {
    }

    Student(const Student &student)
        :firstName(student.firstName), lastName(student.lastName)
    {
    }

    Student(Student &&student)
    {
        firstName=std::move(student.firstName);
        lastName=std::move(student.lastName);
    }

    // ... getters and setters    
};

I use it like this:

std::vector<std::shared_ptr<Student>> students;
std::shared_ptr<Student> stud1 = std::make_shared<Student>("fn1","ln1");
students.push_back(stud1);
Student stud2("fn2","ln2");
students.push_back(std::make_shared<Student>(std::move(stud2)));

From what I have read, the move constructor in automatically generated by the compiler. Right now, when I step into this line students.push_back(std::make_shared<Student>(std::move(stud2))); I reach the move constructor, which is ok.

If I comment out the move constructor when I step into that line I reach the copy constructor. I don't understand why this is happening.

Upvotes: 4

Views: 230

Answers (2)

James McNellis
James McNellis

Reputation: 355019

Visual C++ 2012 does not implicitly generate move constructors or move assignment operators.

(The rules governing when move operations are and are not implicitly declared and defined changed several times during standardization; Visual C++ 2012 does not support the standardized (2011) set of rules.)

Upvotes: 3

Walter
Walter

Reputation: 45414

In your case, you may simple declare all these constructors =default, e.g.

class student
{
  std::string firstname, surname;
public:
  student(student const&) = default;
  student(student&&) = default;
  student&operator=(student const&) = default;
  student&operator=(student&&) = default;
  // etc
};

and don't worry about the details: the compiler should sort this out and generate the appropriate call to std::string::string(string&&) (move constructor).

EDIT Of course, this will not work with deficient compilers, but if you're tagging "C++11", then you should expect a C++11 answer.

Upvotes: 1

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