Initializing an array of pointers in C++

Question

I have a pretty specific data structure issue that I cannot figure out. For my assignment, I must have a dynamically allocated array of structures in my private section of my header. So, up to this point, in my header file, I have

struct node{
  int name;
  node *next;};

In my private, I have

node *adj;

which is, at least to my knowledge, how you would set up having the array.
Then, in my .cpp file, I have

adj = new node*[];

This is throwing a bunch of errors. But, when I have

node *adj[n];

in my cpp and nothing in my header, it works. My questions is how do I have an array in my private section of my header, but dynamically allocate the space in my .cpp?

node *adj; is not an array of pointers, it is a pointer to node. node **adg would be an array of pointers. — Ed Swangren
– Ed Swangren, Commented May 2, 2013 at 5:45
@EdS. The title says array of pointers, the text says array of structures. Having thought about it I guess an array of pointers is what is really required. — john
– john, Commented May 2, 2013 at 5:46

rspencer · Accepted Answer · 2013-05-02 05:41:01Z

2

You have defined

node *adj;

which is a pointer to a node, or an array of nodes. If you want an array of pointers to nodes, you should declare

node **adj;

which is a pointer to a pointer to a node, or an array of pointers to nodes. In the first case, you allocate the array using

adj = new node[n];

which defines an array of nodes. and in the second you use

adj = new node*[n];

which defines an array of node pointers.

adj = new node*[];

should not make sense as it does not tell the compiler how big to make the array.

answered May 2, 2013 at 5:41

rspencer

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1 Comment

marcinx27 Over a year ago

This is exactly what I needed. The second version worked perfectly.

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