CODEWITHSUNDEEP
c++objectpointersnew-operatorinstantiation
Peter
Peter

Reputation: 4161

C++ Pointers and Object Instantiation

This works: 

MyObject *o;
o = new MyObject();

And this does not: 

MyObject o = new MyObject();

Why?

Upvotes: 5

Views: 10876

Answers (3)

MPelletier
MPelletier

Reputation: 16709

The keyword new returns a pointer. It must be assigned to a pointer of an object.

This would also work:

MyObject o = MyObject();

EDIT:

As Seth commented, the above is equivalent to:

MyObject o;

The default constructor (i.e. without parameters) is called if no constructor is given.

Upvotes: 11

bitmask
bitmask

Reputation: 34664

new MyObject() returns a pointer to an object of type MyObject. So really you are trying to assign an object MyObject* (yes, a pointer can be considered an object, too). Thus, you have to declare a variable of MyObject* or something compatible like std::shared_ptr<MyObject>.

The proper initialisation is

// in C++03
MyObject* o(new MyObject());

// in C++11
MyObject* o {new MyObject()};

While the assignment

MyObject* o = new MyObject();

is valid as well.

Upvotes: 4

Andreas Brinck
Andreas Brinck

Reputation: 52549

Because they're not equivalent. Try:

 MyObject* o = new MyObject();

Upvotes: 5

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