realloc() questions

[sl4nted]

I'm making a program that basically takes as input a path and can output the total size of all files/directories inside it. the program recusivly scans through the directory givin and sums up the size of all files in all subfolders. heres the directory structure I've made

struct directory {
        char *name;
        int size;
        int nfiles;
        int ndirs;
        struct directory *parent;
        struct directory **dlist;
        File **flist;
};

in order to put a new directory in **dlist I use this function, which should increase the size of the **dlist member and add the new directory to the list

int dir_add_dir(struct directory *d, struct directory *new)
{
        int ndirs;
        struct directory **temp;

        ndirs = d->ndirs;

        if ((temp = (struct directory **)realloc(d->dlist, sizeof(struct directory *) * (ndirs + 1))) == NULL)
        {
                printf("Memory Error\n");
                return -1;
        }

        d->dlist = temp;
        d->dlist[ndirs] = new;

        d->size += new->size;

        d->ndirs++;

        return 1;
}

d being the parent and new being the directory to add.
I keep getting seg faults though, and when I run it with valgrind it is complaining about the realloc.

am I going about this wrong...or just using realloc wrong. There is no way to tell how many elements will have to go in the list, so it must be updated dynamically.

[jafet]

You're really doing it bad. realloc() may need to copy the entire array over to the new, larger array in case of memory fragmentation. You should be increasing at a fixed rate, say double the array size everytime you fill it. Keep two variables: a size variable for the number of entries in the array, and a capacity vaariable for the maximum number of entries storable before reallocation is required.

Minor issues:
- Don't cast pointers. (See FAQ)
- Extra local ndirs is redundant and occurances can be replaced with d->ndirs without any problems.
- You don't seem to update new->parent. (If I get the usage of parent correctly.)

Anyway, this should do it (not really tested):

struct directory {
        char *name;
        int size;
        int nfiles;
        int ndirs; /* the used size of the array */
        int cdirs; /* the pre-allocated size */
        struct directory *parent;
        struct directory **dlist;
};

int dir_add_dir(struct directory *d, struct directory *new)
{
    struct directory **temp;
    /* if array is full */
    if(d -> ndirs == d -> cdirs)
    {
        if((temp = realloc(d -> dlist, sizeof(struct directory*) * d -> cdirs * 2)) == NULL)
        {
            printf("Memory Error\n");
            return 0;
        }
        d -> dlist = temp;
        d -> cdirs *= 2; /* double capacity of array */
    }
    d -> dlist[d -> ndirs] = new;
    ++d -> ndirs; /* add one to the used size NOT the actual array size */
    d -> size += new -> size;
    new -> parent = d;
    return 1;
}

You might want to check out en.wikipedia.org/wiki/Dynamic_array. If you are also deleting directory entries as well as adding them, you could also add a check to halve the size of the arrays if less than say 1/2 of the array is in use.

[ssharish2005]

why dont u make as a linked list. Do that when u find a new directory inside a directory, create a node of type Directory and link along with the dlink rather than realloc. which is quite more dynamic.

ssharish2005