Datum

Datum is a collection of dynamic and generic data structures implemented from scratch in C with no external dependencies beyond the standard library. It currently features:

Vector: a growable, contiguous array supporting homogenous data types (both primitives and user-defined types);
Map: an associative array that handles generic heterogenous data types;

To learn more about the memory model of this library as well as the technical details on how to use it efficiently and safely, be sure to read the design manual.

Usage

At its simplest, you can use this library as follows:

`Vector`

#include <stdio.h>
#include "src/vector.h"

/*
* Compile with: gcc main.c src/vector.c
* Output: First element: 5
*         Head of vector 6, size is now: 1 
*/ 

int main(void) {
    // Create an integer vector of initial capacity equal to 5
    vector_t *vec = vector_new(5, sizeof(int)).value.vector;

    // Add two numbers
    int val = 5;
    vector_push(vec, &val);
    vector_push(vec, &(int){6}); // Equivalent as above

    // Print 1st element
    const int first = *(int*)vector_get(vec, 0).value.element;
    printf("First element: %d\n", first);

    // Pop second element using LIFO policy
    const int head = *(int*)vector_pop(vec).value.element;
    printf("Head of vector %d, size is now: %zu\n", head, vector_size(vec));

    // Remove vector from memory
    vector_destroy(vec);
    
    return 0;
}

`Map`

#include <stdio.h>
#include "src/map.h"

typedef struct {
    char name[256];
    char surname[256];
    short age;
} Person;

/*
* Compile with: gcc main.c src/map.c
* Output: Name: Bob, Surname: Smith, Age: 34
*/
int main(void) {
    // Create a new map
    map_t *map = map_new().value.map;

    const Person bob = { .name = "Bob", .surname = "Smith", .age = 34 };

    // Add a key to the map
    map_add(map, "bob", (void*)&bob);

    // Retrieve 'Bob' and check if it exists
    map_result_t bob_res = map_get(map, "bob");
    if (bob_res.status == MAP_ERR_NOT_FOUND) {
        puts("This key does not exist.");
    } else {
        const Person *retr = (const Person*)bob_res.value.element;
        printf("Name: %s, Surname: %s, Age: %d\n", retr->name, retr->surname, retr->age);
    }

    // Remove map from memory
    map_destroy(map);

    return 0;
}

For a more exhaustive example, refer to the usage.c file. There, you will find a program with proper error management and a sample usage for every available method. To run it, first issue the following command:

$ make clean all

This will compile the library as well as the usage.c file and the unit tests. After that, you can run it by typing ./usage.

Technical Details

As stated earlier, refer to the design manual for a comprehensive documentation of this library. Below, there's a quick overview about the design choices behind Datum. While both structures use void* to represent values, the way they manage memory is orthogonally different from one another. Let's start with the Map data type.

Map is an hash table implementation that uses open addressing with linear probing for collision resolution and the FNV-1a algorithm as its hashing function. Resizing is performed automatically by doubling the capacity when load factor exceeds 75%. The keys are copied by the hashmap. This means that the hashmap owns them and is responsible to manage their memory. Values, on the other hand, are stored as pointers. This means that the hashmap does NOT own them and the caller is responsible to manage their memory; this includes: allocate enough memory for them, ensure that the pointers remain valid for their whole lifecycle on the map, delete old values when updating a key and, if the values were heap-allocated, free them before removing them or before destroying the map.

Vector, instead, is a dynamic array with generic data type support. This means that you can store any kind of homogenous value on the data structure. As in the Map's case, resizing is performed automatically by increasing the capacity by 1.5 times when the array is full. The dynamic array copies the values upon insertion, thus it is responsible for their allocation and their deletion.

Unit tests

Datum provides some unit tests for both the Vector and the Map data types. To run them, you can issue the following commands:

$ make clean all
$ ./test_vector
$ ./test_map

License

This library is released under the GPLv3 license. You can find a copy of the license with this repository or by visiting the following link.

4.8 KiB Raw Blame History