Declaring 2d array in C++

Question

Hey so I want to declare an 2d array in one of my classes - it is first declared outside of any methods, and then set size by constructor

class xxx
int **triangle;


constructor(int n){
    triangle = new int *[n+1];
    for(int i=0;i<=n; i++) triangle[i]=new int[i+1];
}

but the first line of constructor does not work:

 error: incompatible types in assignment of ‘int**’ to ‘int* [0]’

NVM it's fixed - I put int *triangle[]; in my header file.. 40 minutes wasted :D

Duplicate: http://stackoverflow.com/questions/10007117/how-to-create-a-large-2-dimensional-array-with-c/10007161 — jacekmigacz, Mar 26 '14 at 10:56
It is not what I want - I want to use new. Also it doesn't work aswell: error: incompatible types in assignment of ‘void*’ to ‘int* [0]’ — user3369008, Mar 26 '14 at 10:57
Your code is working for me: http://coliru.stacked-crooked.com/a/8b52e994c4047dfd — Arpegius, Mar 26 '14 at 11:03

score 3 · Answer 1 · answered Mar 26 '14 at 11:03

3

int constructor(int n)
{
    int** triangle = new int*[n + 1];
    for(int i = 0; i <= n; ++i)
        triangle[i] = new int[i + 1];
}

answered Mar 26 '14 at 11:03

jacekmigacz

score 0 · Answer 2 · answered Mar 26 '14 at 14:59

Alternate Solution

Declaring 2D array using std::vector instead of raw pointer

n x n matrix:

 std::vector<std::vector<int> >  triangle( n, std::vector<int>(n, 0) );

row x col matrix

 std::vector<std::vector<int> >  triangle( row, std::vector<int>(col, 0) );

Note: Both the 2d arrays using std::vector are initialized by 0.

2 Answers2