Global multidimensional array of a struct in c

Question

I'm trying to build a simple tournament in c, but I'm struggling to use a multidimensional array of struct round.

typedef struct round{
   enum role  myrole;
   int *opponent;
   int flag;
} *round_t;

static round_t** rounds;

void buildTournament(int players){
   int roundCount = ceil_log2(players);

   rounds = malloc( players * sizeof *rounds );

   size_t row;
   for (row = 0; row < roundCount; ++row)
       rounds[row] = malloc( roundCount * sizeof **rounds );

   int i;
   for (i = 0; i < players; i++)
   {
        for (k = 0; k <= roundCount; k++)
        {
            round_t round = malloc(sizeof(round_t));
            if(i % 2 == 0)
            {
                round->myrole = WINNER;
            }
            else
            {
                round ->myrole = LOSER;
            }
            rounds[i][k] = round;
        }
   }

}

With 8 players, it throws a seg fault writing to rounds[3][0], which is the 10th memory location. This makes me think I'm only allocating 9 memory locations to the array. Obviously, I'm new to C, so any help would be very appreciated.

for (k = 0; k <= roundCount; k++) should be k < roundCount otherwise you index out of bounds for rounds[i][k] — ryanpattison
– ryanpattison, Commented Feb 28, 2015 at 19:29
Thanks, I changed my original implementation which started k at 1 and used rounds[i][k-1] for a simpler explanation for SO. — dhysong
– dhysong, Commented Feb 28, 2015 at 19:58

Community · Accepted Answer · 2017-05-23 12:28:32Z

1

You are not allocating enough space here

round_t round = malloc(sizeof(round_t));

your fault is that you declared round_t as a pointer to a struct round which hides the fact that round_t is struct round * from you, hence sizeof(round_t) seemed natural but it's wrong because it's allocating space for a pointer, and not for a strcut, change it like this

round_t round = malloc(sizeof(*round));

or

round_t round = malloc(sizeof(struct round));

Don't typedef pointers it makes your code very confusing, and if you must typedef a pointer, try to imply that it is a pointer in it's name, something like

typedef struct round{
    enum role  myrole;
    int *opponent;
    int flag;
} round_t;
typedef round_t *round_p;

and also, as @rpattiso commented, you should fix the for loop condition.

edited May 23, 2017 at 12:28

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answered Feb 28, 2015 at 19:29

Iharob Al Asimi

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