Question

I would like to know how to allocate sequential memory for an array of structures inside of another structure. Say I have struct1 which has an array of struct2, I would like to have it all in one sequential block of memory.

I could use malloc to allocate the block, but how would I assign the array’s memory?

struct1 *set = malloc(sizeof(struct1) + sizeof(struct2)*number_of_structs);
set->arr = (struct2*)set + sizeof(struct); //This is probably wrong
set->arr[0].data = 1;
set->arr[1].data = 2; 
...

Thank you.

Answer 1

Use a flexible array member :

#define NUM_ELEM  42

struct a {
   /* whatever */    
};

struct b {
    int c;
    struct a d[];  // flexible array member
};

struct b *x = malloc(sizeof *x + NUM_ELEM * sizeof x->d[0]);