Question

I expect the following code to work. It compiles (gcc), but the executions gives Segmentation fault: 11. How come? Thanks

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

#define MAX_INDEX_LENGTH 20

main()
{
    char **indici;
    int n = 4;

    indici = (char **)malloc(n * sizeof(char*));
    int i;
    for (i = 0; i < n; i++)
    {
        indici[i] = (char *)malloc(MAX_INDEX_LENGTH * sizeof(char*));
    }

    strncpy(indici[0], "aaa", MAX_INDEX_LENGTH);
    strncpy(indici[0], "bbbb", MAX_INDEX_LENGTH);
    strncpy(indici[0], "ccccc", MAX_INDEX_LENGTH);
    strncpy(indici[0], "ddddddd", MAX_INDEX_LENGTH);

    for (i = 0; i < n; i++)
    {
        printf("Index %d is %s\n", n, indici[n]);
    }
}

Answer 1

You’re copying all of the strings into indici[0], so the other 3 are uninitialized.

When you print the uninitialized ones, kaboom.