How to allocate memory for a large two-dimensional array in C?

Question

How to allocate memory for a large two-dimensional array in C?

I'm working with a large two-dimensional array.

In the case where it is 30 x 200 in size, everything counts. At large volumes, the program crashes... I was advised to use memset(), but something doesn't really help... Maybe you have some ideas?

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>

double **B;

int main (int argc, char *argv[])
{ 
    int N, n_A;

    N = 32;
    n_A = 350; /* если сделать n_A = 200, то все работает */
    B = (double **)malloc(N * sizeof(double *));

    for(i = 0; i < N; i++)
    {
        B[i] = (double *)malloc(n_A * sizeof(double));
        memset(B[i], 0, n_A * sizeof(double));
    }

    free(B);

    return 0;
}

3

c массивы память

Author: Grundy, 2011-02-22

Source

3 answers

score 3 · Answer 1

In general, the code is correct, but you need to add a check when allocating memory: this is necessary, because the memory may simply not be enough, and in this case the program will crash, because it will write to non-existent memory. That is, whenever a call to malloc occurs, you must check that the return value is not NULL.

B = (double **)malloc(N * sizeof(double *));

/* Проверить, что память выделена */
if (B != NULL)
{
    for(i = 0; i < N; i++)
    {
        B[i] = (double *)malloc(n_A * sizeof(double));

        /* Проверить, что память выделена */
        if (B[i] != NULL)
        {
            memset(B[i], 0, n_A * sizeof(double));
            free(B[i]);
        }
    }

    free(B);
}

In addition, you must not forget to release the memory allocated by malloc inside the loop, otherwise there will be leaks.

score 1 · Answer 2

All this can be done in one line

double * B;
B = (double *) calloc (N * n_A, sizeof(double));
free (B);

Instead of calling a bunch of functions, you call one that immediately allocates memory for the entire data array and resets it.

The data is accessed using the formula

double a;
a = *(B + i * n_A + j);

Where i is the row number, j is the column number

score 0 · Answer 3

For large volumes, the program crashes...

The local buffer (more precisely, the size of the stack frame) should not be larger than one page. Otherwise, there will be a call outside the watch page of the stack, it will not be expanded, and an exception will occur.