Question

Possible Duplicate:
When should I use the new keyword in C++?

I don’t know the difference between case 1 and case 2:

I define a struct below:

struct Graph {
    int ID;
}

Case 1:

Graph g;
g.ID = 1;

case 2:

Graph* g = new G();
g.ID = 1;

Are these two cases the same? What’s the difference?

Answer 1

In case 1, the memory used by g is allocated on the stack, which means that it will be automatically freed when the function it is in returns.

In case 2, the memory used by g is allocated on the heap, which means that it will only be freed when explicitly deleted using the delete operator.

Also, in case 2 since g is a pointer, you should be accessing fields of g using the -> operator:

g->ID = 1;