Dynamically allocated array using a typedef struct

Question

I've been given this code for a struct:

struct Part /*A Part record*/
{
    int ID;
    float Price;
    int Quantity;
};
typedef Part *Partptr;
// Part record pointer type; The type Partptr becomes synonymous with Part *
typedef Partptr* Index;
// The type Index becomes synonymous with Partptr *

I'm confused on what the typedefs below it are doing. Later in the program, I'm trying to define a dynamically allocated array of this struct using the provided variable Index DBindex , but when I try doing so like this:

DBindex = new Index[];

I get an error:

a value of type "Index *" cannot be assigned to an entity of type "Index"

I thought Index was a pointer, based on the typedef. What am I missing here?

Answer 1

Partptr is an alias for Part* , and Index is an alias for Partptr* (aka Part** ).

Index DBindex = new Index[]; doesn't work, because new returns a T* pointer for whatever type of T it creates, ie:

T* ptr = new T;

T* ptr = new T[size];

So, if DBindex really needs to be an Index (aka Part** ), then you need to new[] a type that is equivalent to Part* , such as Partptr :

Index DBindex = new Partptr[size];

Which is equivalent to:

Part** DBindex = new Part*[size];