How to make all array elements accessible [closed] - c++

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I've been trying to make the elements of an array accessible, but I've had no success so far. This is the code, and I've created it due to the given assignment.
#include<iostream>
#include<iomanip>
#include<cmath>
using namespace std;
class Matrix_1D
{
private:
int *p2values;
int num_elements;
public:
Matrix_1D(int *p2v, int n); // CTOR
~Matrix_1D(); // DTOR
void show();
};
Matrix_1D::Matrix_1D(int *p2v, int n)
{
n = sizeof(p2v)/sizeof(int); // the problem comes from the fact that sizeof(p2v) = 4 bytes, and not the length of the entire array!!!
num_elements = n;
p2values = new int [n];
for(int i = 0; i<num_elements; i++)
p2values[i] = p2v[i];
}
Matrix_1D::~Matrix_1D()
{
delete [] p2values;
}
void Matrix_1D::show()
{
for(int i=0; i<num_elements; i++)
cout << p2values[i] << endl;
}
int main()
{
int array_a[] = {5,3,5};
Matrix_1D fkt_1D_a(array_a, sizeof(array_a)/sizeof(int));
fkt_1D_a.show();
system("pause");
return 0;
}

Answer 1

Matrix_1D::Matrix_1D(int *p2v, int n)
{
n = sizeof(p2v)/sizeof(int); // the problem comes from the fact that sizeof(p2v) = 4 bytes, and not the length of the entire array!!!
num_elements = n;
p2values = new int [n];
for(int i = 0; i<num_elements; i++)
p2values[i] = p2v[i];
}
As you state the sizeof p2v is the size of the pointer so you have no idea how large the array is. Instead, use the parameter that is passed in and don't overwrite it:
Matrix_1D::Matrix_1D(int *p2v, int n)
{
// you don't need the first line at all.
num_elements = n;
p2values = new int [n];
for(int i = 0; i<num_elements; i++)
p2values[i] = p2v[i];
}

Answer 2

The proper C++ way to get the size of your int array is to use a template:
template <typename T, size_t N>
size_t size(T (&)[N]) {
return N; // size of array
}