Two-dimensional array of pointers

Question

I want to write a function that returns pointer to two-dimensional array of pointers. I have this array: Organism* worldTab[20][20]; and my friend advised to write the function I want in this way:

    Organism** getWorldTab() {
    return worldTab[20];
}

Is it correct? When I want to do this (temp is Organism*** temp;):

    *temp = world.getWorldTab();

Visual Studio throws an exception

    Exception thrown: write access violation.

    this->temp was 0xCCCCCCCC.

and I am pretty sure getWorldTab()functions is a problem.

worldTab definition: Organism* worldTab[20][20];

Please read stackoverflow.com/help/mcve and Edit your question — r-sniper
– r-sniper, Commented Apr 21, 2017 at 18:14
It depends on a lot of things, for example the storage class of worldTab. But it's a bad idea in any case. Use std::vector instead of this horrible low-level pointer management. — Christian Hackl
– Christian Hackl, Commented Apr 21, 2017 at 18:15

Quentin · Accepted Answer · 2017-04-21 19:54:05Z

An array is not a pointer, although it can be converted into a pointer to its first element in some situations, and a pointer to an array is completely unlike a pointer to a pointer.

A pointer to your array has the type Organism* (*)[20][20].

A pointer to the first element of the array is probably what your friend had in mind, but that has the type Organism* (*)[20], not Organism** or Organism***, and can't be converted to either.

(And, as a bonus, worldTab[20] is out of bounds because it would be the twenty-first array of the twenty that exist. And you never initialised temp before assigning to *temp, which is the source of the access violation.)

While you could write

Organism* (*getWorldTab())[20] {
    return &worldTab[0];
}

Organism* (*temp)[20] = getWorldTab();

or simply

Organism* (*temp)[20] = worldTab;

I think you should learn to use std::vector and std::array – they relieve a lot of pain.
(Plus, it's 2017. While it can be interesting, there's no need to program like it's 1969.)

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