Question

I’m having a problem figuring out how to initiate an array of struct pointers.
What i bascially want to do is loop through the array of struct pointers and for each pointer i want to do some work.

The code for the structure:

typedef double Align;
union header {
    struct {
        union header * p, *prev;
        unsigned size;
    } s;
    Align x;
};

typedef union header Header;

and the code that i can’t get to work is following:

Header * freelist[NRQUICKLISTS]; /* Listan med  */

void init() { /* call this once in the beginning */
    int i;
    for (i = 0; i < NRQUICKLISTS-1; i++) {
        freelist[i]->s.p = freelist[i]; /* <-- this line cause Segmentation fault */
        freelist[i]->s.size = 0;
    }
    freelist[i] = &base;
    freelist[i]->s.p = freep = &base; /* cirkulär lista */
    freelist[i]->s.size = 0;
}

Answer 1

You need to allocate memory for the pointers before you can use them:

for (i = 0; i < NRQUICKLISTS-1; i++) {
    freelist[i] = new Header;
    freelist[i]->s.p = freelist[i]; /* <-- this line cause Segmentation fault */
    freelist[i]->s.size = 0;
}

Also, I suggest you do it the C++ way – which is using std:vector instead of an array.

Edit:

For C, use malloc:

for (i = 0; i < NRQUICKLISTS-1; i++) {
    freelist[i] = malloc(sizeof(Header));
    freelist[i]->s.p = freelist[i]; /* <-- this line cause Segmentation fault */
    freelist[i]->s.size = 0;
}