Pointer to Pointer to Pointer

Question

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Uses for multiple levels of pointer dereferences?

I was reading another post and this led me to this question. What the heck would something like this mean? Also how deep do people go with a pointer to a pointer to a pointer to a pointer.... I understand Pointer to Pointer but why else you would go more after that? how deep have you gone in using ****?

Foo(SomePtr*** hello);

Solution 1

It is rare in C++ certainly.

In C it may well show up where:

• You use "objects" which are structs, and you always pass them around or create them on the heap as pointers.
• You have collections of such pointers as dynamically allocated arrays thus T** where T is the type.
• You want to get an array so you pass in a T*** and it populates your pointer with a T** (array of T* pointers).

This would be valid C but in C++:

• The first step would be the same. You still allocate the objects on the heap and have pointers to them.
• The second part would vary as you would use vector and not arrays.
• The 3rd part would vary as you would use a reference not a pointer. Thus you would get the vector by passing in vector<T*>& (or vector<shared_ptr<T> >& not T***

Solution 2

You could refer to a 3 dimensional array of ints as int *** intArray;

Solution 3

Well, if your function needs to modify a pointer to a pointer ... ;)

See http://c2.com/cgi/wiki?ThreeStarProgrammer for a discussion.

Solution 4

Pointer to a dynamic array of pointers maybe? Make sense to me.

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Comments

[TOMKA]

I think either DirectX or COM made me go three levels derp.

[secluded]

Hi! Could you please elaborate on what you mean by this?? This is the piece of code I have and I don't understand what's happening: int ***grid; grid = calloc(nx,sizeof(int**)); for (i = 0; i < nx; ++i) { grid[i] = calloc(ny,sizeof(int*)); for (j = 0; j < ny; ++j) { grid[i][j] = calloc(nz,sizeof(int)); } }

[Sam Dufel]

Its allocating a 3d array of ints with dimensions nx, ny, nz.