CODEWITHSUNDEEP
carrays2dmallocexc-bad-access
bellati
bellati

Reputation: 82

2d matrix allocation function segfault (matrix returned by param)

i'm having a problem when trying to write the second row of the matrix (segfault exc_bad_access and kern_invalid_address) allocated with the following function:

Here is my alloc function:

int amatrix(char*** m, const int i, const int j) 
{

    int k;

    (*m) = (char**) malloc(sizeof(char*) * i);
    if ((*m) == NULL) {
        return ERROR;
    }

    for (k = 0; k < i; k++) {
        (*m)[k] = (char*) malloc(sizeof(char) * j);
        if ((*m)[k] == NULL) {
            return ERROR;
        }
    }

    return SUCCESS;
}

I call it by using:

char** matrix;
if (amatrix(&matrix, i, j)) { ...

Edit: As requested:

#define ERROR 00
#define SUCCESS 01

The access where the trouble is:

int gmatrix(char*** m, const int i, const int j)
{
int k, l;

for (k = 0; k < i; k++) {
    for (l = 0; l < j; l++) {
        printf("Matrix[%d][%d] = ", k, l);
        scanf(" %c", m[k][l]);
    }
}

return SUCCESS;
}

Thank you for the quick replies!

Upvotes: 2

Views: 124

Answers (1)

interjay
interjay

Reputation: 110202

Your gmatrix function should take m as a char** parameter, not char***, because it does not need to change its value like amatrix does (only what it points to).

Then you should change the scanf call to:

scanf(" %c", &m[k][l]);

Your current code (with char*** m) doesn't work because m[k] will give undefined behavior when k!=0, because m points only to a single char**.

If m is a char***, the scanf call would need to look like:

scanf(" %c", &(*m)[k][l]);

Upvotes: 2

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