13-Dynamic Object Creation

13.3 new & delete for arrays
new type[size]; // create an array of objects delete [] pointername; //destroy an array • MyType *fp = new MyType[100]; • delete [] fp;
13.4 Running out of storage
13.5 Overloading new & delete
Summary
• new/delete for an object • new/delete for arrays
Exercises
• delete fp;
#include <iostream> using namespace std; class Tree { int height; public: Tree(int treeHeight=0) : height(treeHeight) {} void print() { cout << height<<endl; } }; void main( ) { Tree* t = new Tree(40); t->print(); // 40 delete t; }
• new/new[] returns a pointer that pointer to type. • An object created by new must be destroyed by delete. • A pointer can be destroyed by delete/delete[] only once.
13.1 Object creation
• When a C++ object is created, two events occur: Storage is allocated for the object.
–static storage area –stack –heap ( dynamic memory allocation)


The constructor is called to initialize that storage.
13.2 operator new/delete
new type(initializer); // create a dynamic object delete pointername; // destroy a dynamic object • MyType *fp = new MyType(1,2); • MyType *fp = new MyType;
13 Dynamic Object Creation
Zhao,Qingjie zhaoqj@ Beijing Institute of Technology
• Sometimes you know the exact quantity, type, and lifetime of the objects in your program. But not always. • To solve the general programming problem, it’s essential that you be able to create and destroy objects at runtime. – dynamic memory allocation – heap ( free store) • new, delete
#include <iostream> using namespace std; class Tree { int height; public: Tree(int treeHeight=0) : height(treeHeight) {cout<<"123"<<endl;} void print() { cout << height<<endl; } }; void main( ) { Tree* t = new Tree[3]; t[2]=Tree(40); t[2].print( ); // 40 delete[] t; }