array of structs in C

Question

I'm trying to create an array of structs and also a pointer to that array. I don't know how large the array is going to be, so it should be dynamic. My struct would look something like this:

typedef struct _stats_t
{
 int hours[24]; int numPostsInHour;
 int days[7]; int numPostsInDay;
 int weeks[20]; int numPostsInWeek;
 int totNumLinesInPosts;
 int numPostsAnalyzed;

} stats_t;

... and I need to have multiple of these structs for each file (unknown amount) that I will analyze. I'm not sure how to do this. I don't like the following approach because of the limit of the size of the array:

# define MAX 10
typedef struct _stats_t
{
 int hours[24]; int numPostsInHour;
 int days[7]; int numPostsInDay;
 int weeks[20]; int numPostsInWeek;
 int totNumLinesInPosts;
 int numPostsAnalyzed;

} stats_t[MAX];

So how would I create this array? Also, would a pointer to this array would look something this?

stats_t stats[];
stats_t *statsPtr = &stats[0];

Thanks, Hristo

Answer 1

Use malloc():

http://en.wikipedia.org/wiki/Malloc

Answer 2

The second option of a pointer is good.

If you want to allocate things dynamically, then try:

stats_t* theStatsPointer = (stats_t*) malloc( MAX * sizeof(stats_t) );

as Roland suggests.

Just don't forget to

free(theStatsPointer);

when you're done.

Answer 3

malloc is your friend here.

stats_t stats[] = (stats_t*)malloc(N * sizeof(stats_t));

stats sort of is a pointer to the array. Or you can use stats[3] syntax as if it were declared explicitly as an array.

Answer 4

This is how it is usually done:

int n = <number of elements needed>
stats_t *ptr = malloc (n * sizeof (stats_t));

Then, to fill it in,

for (int j = 0;  j < n;  ++j)
{
   ptr [j] .hours = whatever
   ptr [j] .days = whatever
   ...
}

Answer 5

Based on your replies to other answers it looks like you need a dynamic data structure like a linked list. Take a look at the queue(3) set of facilities.