如何通过C ++中的指针使用3D数组

Question

I'm facing some difficulties with pointers for 3D arrays in C++. I've a array of Q[3][N][N] which I want to pass to a function to print the values at [0][i][j] location (and also for [1][i][j] and [2][i][j]). How can I achieve this? Will it be more convenient to use Q[i][j][0] etc?

for 2D, the following piece of code works just fine when I give &Q[0][0] to the *var:

template <typename T>
void print2d(T *var, int I, int J){
cout << endl;
for (int j = 0; j < J; j++){
    for (int i = 0; i < I; i++){
        cout << setprecision(3) << setw(12) << *(var + (N*i + j));
    }
    cout << endl;
}
cout << endl;
}

I'm using the same approach to write a similar function for 3D which does not write out the correct values: Can anybody let me know the correct way to point to the correct address of Q[i][j][1] . In input argument, I'm giving the address of Q[0][0][0]. Should I use different addresses (such as Q[i][j][1]) if I want to write out for that particular value of k?

template <typename T>
void print3d(T *var, int I, int J, int K){
    cout << endl;
        for (int j = 0; j < J; j++){
            for (int i = 0; i < I; i++){
                cout << setprecision(3) << setw(12) << *(var + I*J*i + I*j + K);
            }
            cout << endl;
        }
    cout << endl;
}

Answer 1

Sample example, N must be const. But consider using vector.

#include <stdio.h>
#include <iostream>
using namespace std;
const int N = 5;

void func2(int* tab, int A, int B, int C)
{
    printf("%d\n", tab[N*N*A + N*B + C] );
}

void func(int tab[3][N][N])
{
    for (int i = 0; i < 3; ++i)
    for (int j = 0; j < N; ++j, printf("\n"))
    for (int k = 0; k < N; ++k)
    {
        printf("%d ", tab[i][j][k]);
    }
}
int main()
{
    int tab[3][N][N];
    int p = 0;
    for (int i = 0; i < 3; ++i)
    for (int j = 0; j < N; ++j)
    for (int k = 0; k < N; ++k)
    {
        tab[i][j][k] = p++;
    }
    func(tab);
    printf("\n");
    func2((int*)tab, 1, 1, 3);
}

Answer 2

I agree with Adam's answer but cant comment, need more points there.

1) Arrays are not pointers. Multidimensional arrays cannot be passed via a pointer, needs to have all but one dimension constant. Here is an answer to help understand.

Cannot cast array to pointer

How do I pass a reference to a two-dimensional array to a function?

http://www.cplusplus.com/forum/articles/17108/

You might want to try vectors from STL instead.

2) Templates are compiled only when there is an instance of it used, that is why its declaration and usage is generally put in one file. Template Compilation