radix sort strings in c (errors) how to solve?

This coding is found on a website. But occuring the errors below:
[Error] invalid conversion from 'void*' to 'bucket_entry*' [-fpermissive]
[Error] invalid conversion from 'void*' to 'bucket*' [-fpermissive]

tried many times already still could not solve.

Code:

---

#include<stdio.h>
#include<string.h>
#include<stdlib.h>

struct bucket_entry
{
    char *str;
    size_t len;
    struct bucket_entry *next;
};
typedef struct bucket_entry bucket_entry;
 
/* A linked list */
struct bucket
{
    bucket_entry *head;
    bucket_entry *tail;
};
typedef struct bucket bucket;
 
/* Initialise buckets */
static void init_buckets(bucket *buckets)
{
    unsigned int b;
    for (b = 0; b < 256; b++) {
        buckets[b].head = NULL;
        buckets[b].tail = NULL;
    }
}
 
/*
 * Turn entries into a linked list of words with their lengths
 * Return the length of the longest word
 */
static size_t init_entries(char **strings, size_t len, bucket_entry *entries)
{
    unsigned int s;
    size_t maxlen = 0;
    for (s = 0; s < len; s++) {
        entries[s].str = strings[s];
        entries[s].len = strlen(strings[s]);
        if (entries[s].len > maxlen) {
            maxlen = entries[s].len;
        }
        if (s < len - 1) {
            entries[s].next = &entries[s + 1];
        }
        else {
            entries[s].next = NULL;
        }
    }
    return maxlen;
}
 
/* Put strings into buckets according to the character c from the right */
void bucket_strings(bucket_entry *head, bucket *buckets, unsigned int c)
{
    bucket_entry *current = head;
    while (current != NULL) {
        bucket_entry * next = current->next;
        current->next = NULL;
        int pos = current->len - 1 - c;
        unsigned char ch;
        if (pos < 0) {
            ch = 0;
        }
        else {
            ch = current->str[pos];
        }
        if (buckets[ch].head == NULL) {
            buckets[ch].head = current;
            buckets[ch].tail = current;
        }
        else {
            buckets[ch].tail->next = current;
            buckets[ch].tail = buckets[ch].tail->next;
        }
        current = next;
    }
}
 
/* Merge buckets into a single linked list */
bucket_entry *merge_buckets(bucket *buckets)
{
    bucket_entry *head = NULL;
    bucket_entry *tail;
    unsigned int b;
    for (b = 0; b < 256; b++) {
        if (buckets[b].head != NULL) {
            if (head == NULL) {
                head = buckets[b].head;
                tail = buckets[b].tail;
            }
            else {
                tail->next = buckets[b].head;
                tail = buckets[b].tail;
            }
        }
    }
    return head;
}
 
void print_buckets(const bucket *buckets)
{
    unsigned int b;
    for (b = 0; b < 256; b++) {
        if (buckets[b].head != NULL) {
            const bucket_entry *entry;
            printf("[%d] ", b);
            for (entry = buckets[b].head; entry != NULL; entry = entry->next) {
                printf("%s", entry->str);
                if (entry->next) {
                    printf(" -> ");
                }
            }
            putchar('\n');
        }
    }
    putchar('\n');
}
 
void print_list(const bucket_entry *head)
{
    const bucket_entry *current;
    for (current = head; current != NULL; current = current->next) {
        printf("%s", current->str);
        if (current->next != NULL) {
            printf(" -> ");
        }
    }
    printf("\n");
}
 
void copy_list(const bucket_entry *head, char **strings)
{
    const bucket_entry *current;
    unsigned int s;
    for (current = head, s = 0; current != NULL; current = current->next, s++) {
        strings[s] = current->str;
    }
}
 
void radix_sort_string(char **strings, size_t len)
{
    size_t maxlen;
    unsigned int c;
    bucket_entry *head;
    bucket_entry *entries = malloc(len * sizeof(bucket_entry)8);
    bucket *buckets = malloc(256 * sizeof(bucket));
    if (!entries || !buckets) {
        free(entries);
        free(buckets);
        return;
    }
    init_buckets(buckets);
    maxlen = init_entries(strings, len, entries);
    head = &entries[0];
    /* Main loop */
    for (c = 0; c < maxlen; c++) {
        printf("Bucketing on char %d from the right\n", c);
        bucket_strings(head, buckets, c);
        print_buckets(buckets);
        head = merge_buckets(buckets);
        print_list(head);
        init_buckets(buckets);
    }
    /* Copy back into array */
    copy_list(head, strings);
    free(buckets);
    free(entries);

int main(void)
{
    char *strings[] = {"The", "quick", "brown", "fox", "jumps", "over", "the", "lazy", "dog"};
    const size_t len = sizeof(strings) / sizeof(char*);
    unsigned int s;
    radix_sort_string(strings, len);
    for (s = 0; s < len; s++) {
        printf("%s\n", strings[s]);
    }
    return 0;
}

---

That error doesn't make sense in C since bucket_entry and bucket are typedefs for struct types, and hence object types, and there is always a valid conversion from void* to a pointer to object type.

What you could be doing is trying to compile this as C++, and if so, the correct solution is to compile this as C instead.

Thank you for your replied. Is it possible let it work in C programming if change some part of this coding?

whats the meaning of [Warning] deprecated conversion from string constant to 'char*' [-Wwrite-strings] ?

Code:

---

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

typedef struct list_entry//typedef:replace old data types into new data types
{
    char *strings;
    size_t len;//represent size of variable in bytes,
              //big enough to represent size of biggest object that system can handle
    list_entry *next;
}list_entry;

typedef struct list
{
    list_entry *head;
    list_entry *tail;
}list;

/*static*/ void initiate(list *lists) //static: if restrict access, then make static, eg: no other file can access this function except file is declared
{
    unsigned int n;//unsigned: no negative number (in ASCII table)
   
    for (n = 0; n < 256; n++)//256 represent all characters in ASCII tables
    {
        lists[n].head = NULL;
        lists[n].tail = NULL;
    }
}

/*static*/ size_t init_entries(char **strings, size_t len, list_entry *entries)//double pointer, address of strings
{
    unsigned int i;//unsigned: no negative number (in ASCII table)
    size_t maxlen = 0;//initialize max length as 0
   
    for (i = 0; i < len; i++)//looping
    {
        entries[i].strings = strings[i];
        entries[i].len = strlen(strings[i]);//size of string [strlen()]
        if (entries[i].len > maxlen)//if entries length more than max length
        {
            maxlen = entries[i].len;//curr max length will replace by curr entries length
        }
        if (i < len - 1)// assume i=0 and len=8, 0<7
        {
            entries[i].next = &entries[i + 1];//0 linked list add next will be 1 linked list add
        }
        else//if > 7,[8],
        {
            entries[i].next = NULL;//8 linked list add will be NULL, cause only total 8 elements
        }
    }
    return maxlen;// for 1st if statement, if didn't match, then max len will not be replaced, and return the original max
}

void list_strings(list_entry *head, list *lists, unsigned int c)
{
    int position;
    unsigned char a;
    list_entry *curr = head;
   
    while (curr != NULL)//if current is not equal to NULL
    {
        list_entry * next = curr->next;
        curr->next = NULL;
        position = curr -> len - c;
        if (position < 0)
        {
            a = 0;
        }
        else
        {
            a = curr->strings[position];
        }
        if (lists[a].head == NULL)
        {
            lists[a].head = curr;
            lists[a].tail = curr;
        }
        else
        {
            lists[a].tail->next = curr;
            lists[a].tail = lists[a].tail->next;
        }
        curr = next;
    }
}

list_entry *merge_lists(list *lists)
{
    list_entry *head = NULL;
    list_entry *tail;
    unsigned int n;
    for (n=0; n<256; n++)
    {
        if (lists[n].head != NULL)
        {
            if (head == NULL)
            {
                head = lists[n].head;
                tail = lists[n].tail;
            }
            else
            {
                tail->next = lists[n].head;
                tail = lists[n].tail;
            }
        }
    }
    return head;
}
 
void print_list(const list_entry *head)
{
    const list_entry *current;
    for (current = head; current != NULL; current = current->next)
    {
        printf("%s", current->strings);
        if (current->next != NULL)
        {
            printf("\t");
        }
    }
    printf("\n\n");
}
 
void copy_list(const list_entry *head, char **strings)
{
    const list_entry *current;
    unsigned int s;
    for (current = head, s = 0; current != NULL; current = current->next, s++)
    {
        strings[s] = current->strings;
    }
}
 
void radix_sort_string(char **strings, size_t len)
{
    size_t maxlen;
    unsigned int c;
    list_entry *head;
    list_entry *entries = (list_entry*)malloc(sizeof(list_entry) * len);
    list *lists = (list*)malloc(sizeof(list) * 256);
    if (!entries || !lists)
    {
        free(entries);
        free(lists);
        return;
    }
    initiate(lists);
    maxlen = init_entries(strings, len, entries);
    head = &entries[0];
   
    for (c = 1; c <= maxlen; c++)
    {
        printf("Sorting on char %d from the right:\n", c);
        list_strings(head, lists, c);
        head = merge_lists(lists);
        print_list(head);
        initiate(lists);
    }
    copy_list(head, strings);
    free(lists);
    free(entries);
}

int main()
{   
    char *strings[]={"kitten","puppy","sheep","birds","mouse","snake","ants"};
    const size_t len = sizeof(strings) / sizeof(char*);
    size_t maxlen;
   
    radix_sort_string(strings, len);
    return 0;
}

---

> Is it possible let it work in C programming if change some part of this coding?
Normally, you rename your prog.cpp file to be prog.c
Then the compiler will automatically know it's a C program.

Then you can get rid of the casts on your malloc return values.

> whats the meaning of [Warning] deprecated conversion from string constant to 'char*' [-Wwrite-strings] ?
Then change to this
const char *strings[]=...

and propagate the const-correctness through all your functions and other pointers.

Thank you !