Complete code for Understanding and implementing a Hash Table (in C) by Jacob Sorber

hashtable_external.c

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

#define MAX_NAME 256
#define TABLE_SIZE 10

typedef struct {
    char name[MAX_NAME];
    int age;
    //...and other stuff later, maybe
    struct person *next;
} person;

person * hash_table[TABLE_SIZE];

unsigned int hash(char *name) {
    int length = strnlen(name, MAX_NAME);
    unsigned int hash_value = 0;
    for (int i=0; i < length; i++) {
        hash_value += name[i];
        hash_value = (hash_value * name[i]) % TABLE_SIZE;
    }
    return hash_value;
}

bool init_hash_table() {
    for (int i=0; i < TABLE_SIZE; i++) {
        hash_table[i] = NULL;
    }
    //table is empty
}

void print_table() {
    printf("Start\n");
    for (int i = 0; i < TABLE_SIZE; ++i)
    {
        if (hash_table[i] == NULL)
        {
            printf("\t%i\t---\n", i);
        } else {
            printf("\t%i\t", i);
            person *tmp = hash_table[i];
            while (tmp != NULL) {
                printf("%s - ", hash_table[i]);
                tmp = tmp->next;
            }
            printf("\n");
        }
    }
    printf("End\n");
}

bool hash_table_insert(person *p) {
    if (p == NULL) return false;
    int index = hash(p->name);
    p->next = hash_table[index];
    hash_table[index] = p;
    return true;
}

person *hash_table_lookup (char *name) {
    int index = hash(name);
    person *tmp = hash_table[index];
    while (tmp != NULL &&
            strncmp(tmp->name, name, MAX_NAME) != 0) {
        tmp = tmp->next;
    }
    return tmp;
}

person *hash_table_delete(char *name) {
    int index = hash(name);
    person *prev = NULL;
    person *tmp = hash_table[index];
    while (tmp != NULL &&
            strncmp(tmp->name, name, MAX_NAME) != 0) {
        prev = tmp;
        tmp = tmp->next;
    }
    if (tmp == NULL) {
        return NULL;
    }
    if (prev == NULL) {
        hash_table[index] = tmp->next;
    } else {
        prev->next = tmp->next;
    }
    return tmp;
}

int main(int argc, char const *argv[])
{
    init_hash_table();
    print_table();

    person jacob = {.name="Jacob", .age=256};
    person kate = {.name="Kate", .age=27};
    person moph = {.name="Mpho", .age=14};
    person sarah = {.name="Sarah", .age=54};
    person edna = {.name="Edna", .age=15};
    person maren = {.name="Maren", .age=25};
    person eliza = {.name="Eliza", .age=34};
    person robert = {.name="Robert", .age=1};
    person jane = {.name="Jane", .age=75};

    hash_table_insert(&jacob);
    hash_table_insert(&kate);
    hash_table_insert(&moph);
    hash_table_insert(&sarah);
    hash_table_insert(&edna);
    hash_table_insert(&maren);
    hash_table_insert(&eliza);
    hash_table_insert(&robert);
    hash_table_insert(&jane);
    print_table();

    person *tmp = hash_table_lookup("Mpho");

    if (tmp == NULL) {
        printf("Not found!\n");
    } else {
        printf("Found %s.\n", tmp->name);
    }

    hash_table_delete("Mpho");
    tmp = hash_table_lookup("Mpho");
    if (tmp == NULL) {
        printf("Not found!\n");
    } else {
        printf("Found %s.\n", tmp->name);
    }
    print_table();

    // printf("Jacob => %u\n", hash("Jacob"));
    // printf("Natalie => %u\n", hash("Natalie"));
    // printf("Sara => %u\n", hash("Sara"));
    // printf("Mpho => %u\n", hash("Mpho"));
    // printf("Tebogo => %u\n", hash("tebogo"));
    // printf("Ron => %u\n", hash("Ron"));
    // printf("Jane => %u\n", hash("Jane"));
    // printf("Maren => %u\n", hash("Maren"));
    // printf("Bill => %u\n", hash("Bill"));
    return 0;
}