Error in filling static array dynamically in C

Question

I have to use a static two-dimensional array and a dynamic matrix as a part of my college task. So, I've created them, and now trying to fill and then print them to a console, but getting "segmentation fault". That's how I'm trying to achieve it:

#include "arrayutils.h"
#include <stdlib.h>
#include <stdio.h>

#define ROWS 5
#define COLUMNS 7

int main3() {
    /*init static array*/
    double twodimarray[ROWS][COLUMNS];

    /*init dynamic array*/
    double **matrix = (double**) malloc(sizeof(double*) * ROWS);
    for(int i = 0; i < ROWS; i++) *(matrix + i) = (double*)malloc(sizeof(double) * COLUMNS);

    for(int i = 0; i < ROWS; i++){
        dfillarran(*(matrix + i), COLUMNS);
        dfillarran(twodimarray[i], COLUMNS);
    }

    puts("Dynamic matrix :");
    printmx(matrix, ROWS,COLUMNS);

    puts("Static array:");
    printmx(twodimarray, ROWS, COLUMNS);

    /*freeing mem*/
    for(int i = 0; i < ROWS; i++) free(*(matrix + i));
    free(matrix);
}

Error is definitely in function printmx(), but I can't understand why; It works for dynamic matrix, and fails only for static one, but static array name - is a pointer to array of pointers, where each one is pointing array of values, just like dynamic one!
There is code of my printmx() function from arrayutils.h:

/**Print Matrix*/
void printmx(double** mx, int rows, int col){
    for(int i = 0; i < rows; i++) {
        for(int j = 0; j < col; j++){
            printf("%.lf ", *(*(mx + i)+j));
        }
        putchar('\n');
    }
    putchar('\n');
}

Funcion that fills arrays with random values can be found here, in arrayutils.c, that I've created for all other tasks that use same functions like filling and printing arrays, but I don't think, that problem is there..
Probably, I'm wrong somewhere in theory, and still not getting the difference between static and dynamic matrix, please correct me :)

p.s.There is a screenshot of the error:

@ScottHunter as I said above, there is "segmentation fault" (updated question with screenshot). — OldTeaOwl
– OldTeaOwl, Commented Dec 23, 2019 at 17:35
a dynamic matrix? double **matrix does not refer to a matrix. It refers to an array of pointers to multiple, separate one-dimensional arrays. See Correctly allocating multi-dimensional arrays. Read that and you'll see why your code failed. — Andrew Henle
– Andrew Henle, Commented Dec 23, 2019 at 17:39
*(*(mx + i)+j) is better written as mx[i][j]. There is no other difference besides the former looking uglier, being harder to read and perceived less professional. — Antti Haapala
– Antti Haapala, Commented Dec 23, 2019 at 21:27

Vlad from Moscow · Accepted Answer · 2019-12-23 17:31:30Z

3

The function printmx may not be called for the two objects of different types.

The array twodimarray is a two dimensional array that when is passed to the function has the type double ( * )[COLUMNS].

While matrix is a pointer of the type double **.

edited Dec 23, 2019 at 17:31

answered Dec 23, 2019 at 17:24

Vlad from Moscow

313k27 gold badges204 silver badges358 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Error in filling static array dynamically in C

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related