Toy Hash Map in C

A simple implementation of a hash map (hash table) with chaining in C.
Supports string keys and integer values, with O(1) average insertion and lookup.

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Features

• Hash map with chaining for collision resolution.
• String keys (up to 100 characters).
• Dynamic memory allocation for nodes.
• Safe insertion using strncpy to avoid buffer overflow.
• Lookup returns a pointer to the stored value.
• Proper memory cleanup with freeMap().

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Files

File	Description
common.h	Header file defining hashmap, node, and product structs, and function prototypes.
main.c	Contains hash(), initMap(), insert(), lookup(), freeMap(), and a sample main() to test the hash map.

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Usage

1️ Compile

gcc main.c -o main

2️ Run

./main

Expected output:

banana: 20

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Example Code

hashmap myMap;
initMap(&myMap, 16);

insert("apple", 10, &myMap);
insert("banana", 20, &myMap);

int* val = lookup(&myMap, "banana");
if (val) printf("banana: %d\n", *val);

freeMap(&myMap);

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How it Works

1. Hashing
   • Computes hash of a string key using:

     hash = 0;
     for each char c: hash = hash * 31 + c
     index = hash % capacity

2. Collision Resolution
   • Uses chaining: each bucket is a linked list of nodes.
   • New nodes are inserted at the head of the linked list.
3. Memory Management
   • Buckets array is allocated using calloc → all pointers initialized to NULL.
   • Each node is dynamically allocated.
   • freeMap() cleans all nodes and the buckets array.

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Limitations

• Fixed maximum key length (100 characters).
• No dynamic resizing of the hash table.
• Only supports integer values.

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Possible Improvements

• Support for arbitrary-length strings using dynamic allocation.
• Dynamic resizing of buckets when load factor > 0.75.
• Support for generic values using void*.
• Better hash functions (e.g., DJB2, FNV-1a).

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License

This project is MIT licensed.