"C + + Primer 12th Chapter" Unique_ptr

Unique_ptr

• a unique_ptr owns the objects it manages, and unlike shared_ptr, Unique_ptr points to an object that can have only one user . When the unique_ptr is destroyed, the object it points to is also destroyed.

• Unlike shared_ptr, no make_shared_ptr-like standard function returns a unqiue_ptr, when a unique_ptr is defined, it needs to be bound to a pointer returned by new, like shared_ptr, Initialization unique_ptr must take the form of direct initialization:

unique_ptr<double> p1;              // P1 points to a double type  variable unique_ptr<int> P2 (newint(1024x768));  // P2 points to an int type with a value  of 1024x768 •

• because only one unique_ptr owns the object it points to, Unique_ptr does not support normal copy or assignment operations.

Unqiue_ptr operation

Although we cannot copy or assign Unqiue_ptr, we can transfer the ownership of the pointer from one unqiue_ptr to another by calling release:

// transfer ownership from P1 (point to String Stegosaurus) to P2unqiue_ptr<string> P2 (p1.release ())      // release set P1 to null nqiue_ptr<string> P3 (thenewstring("Trex " ));p 2.reset (P3.release ())    //  Reset released the memory                          that the P2 originally pointed to //  Reset releases the memory it originally pointed to

Pass to the Unique_ptr parameter and return unique_ptr

• Although you cannot copy a unique_ptr, with one exception, we can copy or assign a unique_ptr that will be destroyed, such as returning a unique_ptr:

unique_ptr<int> Clone (int  p) {    return unique_ptr<int> (newint(P));}  

You can also return a copy of a local variable:

unique_ptr<int> Clone (int  p) {    unique_ptr<int> RET ( New int (P));       return ret;    }  

Note : For two pieces of code, the compiler knows that the object to be returned will be destroyed. In this case, the compiler performs a special copy.

"C + + Primer 12th Chapter" Unique_ptr