Question

#include <iostream>
#include <vector>

using namespace std;

struct s_Astruct {
    vector <int> z;
};


int main () 
{

    vector <s_Astruct> v_a;

    for(int q=0;q<10;q++)
    {
        v_a.push_back(s_Astruct());
        for(int w =0;w<5;w++)
            v_a[q].z.push_back(8);
    }

    vector <s_Astruct> * p_v_a = & v_a;
    cout << p_v_a[0]->z[4]; //error: base operand of '->' has non-pointer type 
                     //'__gnu_debug_def::vector<s_Astruct, std::allocator<s_Astruct> >'


}

There seems to be some issue with this sort of operation that I don’t understand. In the code that I’m working on I actually have things like p_class->vector[]->vector[]->int; and I’m getting a similar error.

Answer 1

You want to do this:

cout << ((*p_v_a)[0]).z[4];

What you are doing is dereferencing the pointer by using [] and grabbing the 0’th offset, and then trying to dereference the non-pointer.

Another way to do it (which is just ugly):

cout << (p_v_a[0][0]).z[4];