Creating an array of pointers to other pointers

Question

So how would I create an array which would contain pointers to other arrays, so that I can still access the arrays that the overall array points to? I tried this:

#include <iostream>

using namespace std;

int main (void)
{

bool (*arrays)[3], *arr1, *arr2, *arr3, *tempArr;

arr1 = new bool[2];
arr2 = new bool[2];
arr3 = new bool[2];

arr1[0] = arr2[0] = arr3[0] = 0;
arr1[1] = arr2[1] = arr3[1] = 1;

arrays[0] = arr1;
arrays[1] = arr2;
arrays[2] = arr3;

int n = 0;

while (n <= 2) {

    tempArr = arrays[n];

    cout << tempArr[0] << tempArr[1] << "\n";
}
}

Also, how would I make the overall array ("arrays") a pointer so that I can add new arrays to it? I made a preliminary function, but it doesn't work (note "paths" is the overall array):

void addPath (void)
{

int n = getArrayLength(paths), i = 0;
bool (*newPaths)[n + 1];

while (i < n) {

    newPaths[i] = paths[i];

    ++i;
}

delete [] paths;

newPaths[n] = tempPath;

paths = newPaths;
}

Hopefully this isn't to confusing or absurd, and thank you for your help.

Possible duplicate of any of the dozens of questions that appear if you search for "c++ array of pointers" — Brian Roach
– Brian Roach, Commented Apr 7, 2011 at 21:53

Jerry Coffin · Accepted Answer · 2011-04-07 21:55:41Z

1

It appears that you're looking for std::vector:

#include <vector>

std::vector<std::vector<bool> > paths;

Note, however, that std::vector<bool> isn't a normal "container", and doesn't support all the operations of a normal container like vector<any_type_other_than_bool> would.

answered Apr 7, 2011 at 21:55

Jerry Coffin

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Comments

AVH · Accepted Answer · 2011-04-07 22:05:31Z

You could use malloc. Of course, that's kind of C code, not C++:

#include <cstring>
#include <cstdlib>

size_t ptrArraySize = 3; 
bool** arrays = (bool**) malloc(ptrArraySize * sizeof(bool*));

Or, you could do as Jerry Coffin suggested. However, this doesn't give you a vector with pointers to vectors. It gives you a vector of vectors (so stack allocated, not on the heap). To get a vector of pointers to vectors, you could do something like:

#include <vector>

std::vector<std::vector<bool> * > ptrVector;
std::vector<bool> * vectorA = new std::vector<bool>();
vectorA->push_back(true);
ptrVector.push_back(vectorA);

Another possibility is using one of boost::scoped_array or boost::shared_array, depending on your needs.

Chris Dodd · Accepted Answer · 2011-04-07 22:47:14Z

0

bool (*arrays)[3] declares arrays to be a pointer to an array of 3 bools -- you want an array of 3 pointers to bools, or bool *arrays[3]. To make a pointer to that dynamically, you want just bool **arrays = new bool*[3];

answered Apr 7, 2011 at 22:47

Chris Dodd

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