Accessing variables from a struct

c++ pointers indirection
Zeeshan Rang picture Zeeshan Rang · Sep 3, 2009 · Viewed 8.6k times · Source

How can we access variables of a structure? I have a struct:

typedef struct {
   unsigned short a;
   unsigned shout b;
} Display;

and in my other class I have a method:

int NewMethod(Display **display)
{
   Display *disp=new Display();
   *display = disp;
   disp->a=11;
}

What does **display mean? To access variables of struct I have used ->, are there other methods too?

Answer

unwind picture unwind · Sep 3, 2009

As Taylor said, the double asterisk is "pointer to pointer", you can have as many levels of pointers as you need.

As I'm sure you know, the arrow operator (a->b) is a shortcut for the asterisk that dereferences a pointer, and the dot that accesses a field, i.e.

a->b = (*a).b;

The parentheses are necessary since the dot binds tighter. There is no such operator for double asterisks, you have to first de-reference to get to the required level, before accessing the fields:

Display **dpl = ...;

(*dpl)->a = 42;

or

(**dpl).a = 42;

Related questions

What are the differences between a pointer variable and a reference variable in C++?

I know references are syntactic sugar, so code is easier to read and write. But what are the differences?

Read More
Return array in a function

I have an array int arr[5] that is passed to a function fillarr(int arr[]): int fillarr(int arr[]) { for(...); return arr; } How can I return that array? How will I use it, say I returned a pointer how am …

Read More
Regular cast vs. static_cast vs. dynamic_cast

I've been writing C and C++ code for almost twenty years, but there's one aspect of these languages that I've never really understood. I've obviously used regular casts i.e. MyClass *m = (MyClass *)ptr; all over the place, but there …

Read More