array of struct pointers

jellyKing · 04-12-2003

i have a function which creates an array of pointers to a struct like:

Code:

node *fn()
{
       node *buf[MAX];
       <other code here>
       printf("buf:%d\n",buf[0]->num);
       printf("buf:%d\n",buf[0]->next->num);
       printf("buf:%d\n",buf[1]->num);
       printf("buf:%d\n",buf[1]->next->num);
       return *buf;
}

main()
{
        node *control=fn();
        printf("%d\n",control->num);
        printf("%d\n",control->next->num);
        control++;
        printf("%d\n",control->num);
        printf("%d\n",control->next->num);
}

the problem is my printf's from main and from f() do not match..i do not understand why. The ones I see from f() are correct but the ones from main are not. why is this?

**Scarlet7** · 04-12-2003

The node pointer array in fn() is allocated from the local stack and will be lost when returned from fn(). You need to allocate memory for the pointer array. You need to return as a pointer array i.e ** If you're going to use as an array of node pointers. The 'control' memory needs to freed at some point when finished with.
It would be best to pass the pointer array to fn() in the first place if its a fixed size and not return anything.

Code:

node **fn()
{
       node **buf;  
       buf = (node **) malloc(sizeof(node **)*MAX);

       <other code here>
       printf("buf:%d\n",buf[0]->num);
       printf("buf:%d\n",buf[0]->next->num);
       printf("buf:%d\n",buf[1]->num);
       printf("buf:%d\n",buf[1]->next->num);
       return buf;
}
main()
{
        node **top=fn();
        node **control=top;

        printf("%d\n",(*control)->num);
        printf("%d\n",(*control)->next->num);
        control++;
        printf("%d\n",(*control)->num);
        printf("%d\n",(*control)->next->num);

        free(top);
       
       return 0;
}

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