new matrix[N][N] failure

Question

I'm having a stack overflow allocating a huge matrix on the stack (and I agree with that: it's stupid to allocate it there) and I'm writing the following code since I want to access the matrix's elements with the subscripts indices mat[x][y]

double (*mul1)[N][N];
mul1 = new double[N][N];

I'm receiving an error:

error C2440: '=' : cannot convert from 'double (*)[1000]' to 'double(*)[1000][1000]'

Why can't I allocate a bidimensional array with new?

This is actually slightly different from the question someone linked as duplicate, because (I assume) N is known at compile time. You can do it with `double (*mul1)[N];` and you avoid the pointer indirection that appears in the linked question for the nested arrays. (The key is that the `*` _replaces_ one of the `[]`, and `new T[]` returns a pointer to the first element.) Or you can write `unique_ptr mul1(new double[N][N]);` and get automatic cleanup. — entheh, Mar 23 '13 at 11:28

score 2 · Answer 1 · answered Mar 23 '13 at 11:23

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You can do it like so:

int N = 10 ;
double** mul1 = new double*[N];
for(int i = 0; i < N; ++i)
   mul1[i] = new double[N];

answered Mar 23 '13 at 11:23

Shafik Yaghmour

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score 1 · Accepted Answer · edited May 23 '17 at 12:22

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double *mul1[N];
for (int i=0;i<N;++i)
    mul1[i] = new double[N];

Representing a 2D array as a 1D array

Performance of 2-dimensional array vs 1-dimensional array

edited May 23 '17 at 12:22

Community

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answered Mar 23 '13 at 11:22

0x90

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error C2440: '=' : cannot convert from 'double (*)[1000]' to 'double **' – Johnny Pauling Mar 23 '13 at 11:25

new matrix[N][N] failure

2 Answers2

Linked