My program crashes when using free function (C) on array

Question

My program works if I don't free the memory I allocated dinamically, but when I try to free it, it crashes. I am running my code on Dev-C++ and the error message is not helpful: a problem has made the program stop working. The problem is at the end of the code. If I take of the freeing part, the program works just fine. Here is a sample input:

5
2.3
1.4 8.2
3.1 2.0 7.7
5.3 6.1 4.4 1.2
5.5 6.1 3.0 2.3 4.9 

The code:

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

int main(void) {
    int ordem;
    scanf("%d", &ordem);
    double **vetor; //apontador para apontador (jagged array)
    double soma = 0;
    int elementos;
    elementos = (ordem*ordem + ordem) / 2;
    vetor = malloc(ordem * sizeof(double*));   //o primeiro endereço do vetor é seu local de memória, que define quantos pointers ele terá (ordem)
    int n, m;
    for (n = 0; n < ordem; n++) {
        *(vetor + n) = malloc(n * sizeof(double));
    }
    for (n = 0; n < ordem; n++) {
        for (m = 0; m <= n; m++) {
            scanf("%lf", *(vetor + n) + m);
            soma = soma + *(*(vetor + n) + m);
        }
    }
    double media = soma / (double) elementos;
    double aux = 0;
    for (n = 0; n < ordem; n++) {
        for (m = 0; m <= n; m++) {
            aux = aux + pow((media - vetor[n][m]), 2);
        }
    }
    double desvio = sqrt(aux / ((double)elementos));
    for (n = 0; n < ordem; n++) {
        for (m = 0; m <= n; m++) {
            printf("%.12lf ", (vetor[n][m] - media) / desvio);
        }
        printf("\n");
    }
    printf("\n%.12lf %.12lf \n", media, desvio);

    for (n = 0; n < ordem; n++) {
        free(*(vetor + n));
    }
    free(vetor);

    return 0;
}

And that's pretty much it. I don't know how to fix this. I don't think dealloc has the same effect. I prefer to stick to free. New information I discovered: for the sample input, I can free((vetor + 0)), ((vetor + 1)) and (*(vetor + 2)), but not 3 and 4. That means the vector somehow has a problem on these two.

Answer 1

You have already received your answer, but there are several other areas where you really need to validate your input and allocations if you are going to have any confidence your code is working with actual values and not writing off into unknown parts of your hardware's memory. Always, always, validate user input and memory allocation. Just a few extra lines of code can help, e.g.:

int ordem;
if (scanf ("%d", &ordem) != 1) {
    fprintf (stderr, "error: invalid input (ordem)\n");
    return 1;
}
double **vetor,
       soma = 0;
int elementos, n, m;

elementos = (ordem * ordem + ordem) / 2; 
if (!(vetor = malloc (ordem * sizeof *vetor))) {
    fprintf (stderr, "error: virtual memory exhausted.\n");
    return 1;
}

for (n = 0; n < ordem; n++)
    if (!(*(vetor + n) = malloc ((n + 1) * sizeof **vetor))) {
        fprintf (stderr, "error: virtual memory exhausted.\n");
        return 1;
    }

for (n = 0; n < ordem; n++) {
    for (m = 0; m <= n; m++) {
        if (scanf ("%lf", *(vetor + n) + m) != 1)  {
            fprintf (stderr, "error: invalid input (vetor + %d)\n", n);
            return 1;
        }
        soma = soma + *(*(vetor + n) + m);
    }
}

Good luck with your coding.

Answer 2

Change this:

for (n = 0; n < ordem; n++) {
    *(vetor + n) = malloc(n * sizeof(double));
}

to this:

for (n = 0; n < ordem; n++) {
    *(vetor + n) = malloc((n + 1) * sizeof(double));
}

The reason is that n is ZERO in the first iteration, so you are requesting malloc() to allocate zero bytes for you..

BTW, here is what I usually use for not making such kind of mistakes: 2d-dynamic-array-c.

Output:

C02QT2UBFVH6-lm:~ gsamaras$ gcc -Wall main.c 
C02QT2UBFVH6-lm:~ gsamaras$ ./a.out
5
2.3
1.4 8.2
3.1 2.0 7.7
5.3 6.1 4.4 1.2
5.5 6.1 3.0 2.3 4.9
-0.892202112506 
-1.307537578672 1.830552610141 
-0.523015031469 -1.030647267895 1.599810684493 
0.492249441383 0.861436522419 0.076913975216 -1.399834348932 
0.584546211642 0.861436522419 -0.569163416599 -0.892202112506 0.307655900864 

4.233333333333 2.166923061753
C02QT2UBFVH6-lm:~ gsamaras$