How to pass by pointer a multidimentional vectors using pointers in C++?

Question

I want to print the values of the multi-dimensional vector a using pass by pointer. Can anyone please let me know what is wrong in my program? I am getting a lot of errors.

#include <iostream>
#include <vector>

using namespace std;

class foo{
    private:
    vector <int> v;
    public:
    foo(vector<vector <int> >**);
};

foo :: foo(vector<vector<int> >** a)
{
    cout << a[0][0] <<endl;
    
    //cout<<a->size()<<endl;
}

int main()
{
    vector<vector<int>> a{{1,2,3,4},{5,6,7,8}};
    foo f(&a);
    
}

Thank you!

Please show the errors you are getting. You aren't passing by reference you are using pointers so you need to use `(*a)[0][0]` — Alan Birtles, Oct 21 '20 at 06:13
It looks like you've been reading about arrays and are trying to apply what you read to vectors. Get a [good book](https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list). (And there is absolutely no reason to use a class here.) — molbdnilo, Oct 21 '20 at 06:16
@molbdnilo Actually this class structure is used in a different program that I am writing. Yes this class is not needed here but I need this concept in a different program. And yes I am tryng to replicate the multi dimensional array thing in vectors. — uuuuuuuuuu, Oct 21 '20 at 06:20

score 2 · Accepted Answer · answered Oct 21 '20 at 06:14

You are confusing some things here:

vector<vector<int> >** is a pointer to a pointer of vector<vector<int> >.
In foo f(&a); the expression &a is vector<vector<int> >* (pointer to vector of vectors of int)
A reference would be vector<vector<int> > &.

You would have foo like this:

//     Reference here VVV
foo(vector<vector<int> > &a)

and simply call like this:

foo f(a);

(without taking the address of a)

How to pass by pointer a multidimentional vectors using pointers in C++?

1 Answers1