Thread: How to access functions from another class in C++?

I am trying to create a class called array whic is based on class vector. I use the template class for generalized data type and some constructors to reserve the memory for the array.
I ran into those error without any idea how to fix them. Please help me to explain the error and instruct me to fix them. Thanks

main.cpp: In function ‘int main(int, char**)’:
main.cpp:11:22: error: ‘class array<int>’ has no member named ‘size’
main.cpp:12:6: error: no match for ‘operator[]’ in ‘a[m]’
main.cpp:13:22: error: no match for ‘operator[]’ in ‘a[m]’
Compilation failed.

----------------------------------------------------------------------

Code:

#ifndef ARRAY_H
#define ARRAY_H

#include <string>           //for std::string
#include <vector>           //for std::vector

template <typename T> 
class array 
{
private: 
    size_t N1,N2,N3;
    std::vector<T> array1D; 
    std::vector<std::vector<T> > array2D; 
    std::vector<std::vector<std::vector<T> > > array3D;         
public:    
       // default constructor
    array();
    array(size_t); 
    array(size_t,size_t);
    array(size_t,size_t,size_t);
        
};
#endif
--------------------------------------------------------------

# include "array.h"

template <typename T> 
array<T>::array(size_t i)
{
    N1 = i;
    // make room for some elements
    array1D.reserve(N1);
}

template <typename T> 
array<T>::array(size_t i,size_t j)
{
    N1=i;
    N2=j;
    array2D.reserve(N1);
    for (int m=0; m < array2D.size(); m++)
        array2D[m].reserve(N2);        
}

-------------------------------------------------------
#include <iostream>            //for std::cout
#include <vector>           //for std::vector
#include "array.h"

int main(int argc, char * argv[])
{
    size_t i=10;
    array<int> a(i);
    
    for (int m=0; m < a.size(); m++) {
        a[m]=m;
        std::cout << a[m] << '\n';
    }
    return 0;
}

Hi Elysia,
Yes, this is just my practice since I am new to OOP. I'm trying to figure out how to use the member function size and operator [] from vector class for this array class (just like the tittle of this thread). Is there any other way to achieve that?
Thanks.

You would have to write the size() function yourself if you wanted to use it in your array class. Basically just make sure that your member function always returns the right value for that.

Using [] is possible for user-defined classes like your array class - it involves something called "operator overloading" which is a very searchable term. There are many sources that can help you implement it properly, if you want to tackle that now. Try reading Overloading the Subscript Operator the Right Way. A lot of operator overloading is typing out the right function, but there are some rules of thumb to consider.

@whiteflags, Thanks!!! Your answer is very helpful.