Structured Types

Commonly used object and collection types in JavaScript and their mapping to C.

JavaScriptC
array(The type of an array varies with types)

Array

Fixed arrays are supported the same way in C as in JavaScript.

JavaScript:

let someArray = [1,2];

C:

int someArray[2] = {1, 2};

List

In C the equivalent of a array is an array.

JavaScript:

let something = ["a", "b"];
something.push("c");

c:

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

int main() {
    char **something = malloc(2 * sizeof(char*));
    something[0] = "a";
    something[1] = "b";
    int size = 2;
    
    // Before adding an element
    for (int i = 0; i < size; i++) {
        printf("%s ", something[i]);
    }
    
    // Adding an element
    char *new_element = "c";
    size++;
    char **temp = realloc(something, size * sizeof(char*));
    if (temp != NULL) {
        something = temp;
        something[size - 1] = new_element;
    }
    
    // After adding an element
    printf("\n");
    for (int i = 0; i < size; i++) {
        printf("%s ", something[i]);
    }
    
    // Release the memory.
    free(something);
    
    return 0;
}

Tuples

JavaScript:

const let something = [1, 2];
console.log(`a = ${something[0]} b = ${something[1]}`);

In C, arrays are used to simulate the concept of tuples:

#include <stdio.h>

int main() {
    int something[] = {1, 2};
    printf("a = %d b = %d", something[0], something[1]);
    return 0;
}

// deconstruction supported
#include <stdio.h>

int main() {
    // Define a tuple
    struct Tuple {
        int a;
        int b;
    };

    // Initialize the tuple
    struct Tuple something = {1, 2};

    // Deconstruct tuples
    int a = something.a;
    int b = something.b;
    printf("a = %d b = %d\n", a, b);

    return 0;
}

NOTE: C tuple elements cannot be named. The only way to access a tuple element is by using the index of the element or deconstructing the tuple.

Dictionary

In C the equivalent of a Dictionary is a object.

JavaScript:

var something = {
    "Foo": "Bar",
    "Baz": "Qux"
};

something["hi"] = "there";

C:

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

#define INITIAL_CAPACITY 2

typedef struct {
    char* key;
    char* value;
} Entry;

typedef struct {
    Entry* entries;
    int capacity;
    int size;
} HashMap;

void insert(HashMap* map, char* key, char* value) {
    if (map->size >= map->capacity) {
        map->capacity *= 2;
        map->entries = realloc(map->entries, map->capacity * sizeof(Entry));
    }
    map->entries[map->size].key = strdup(key);
    map->entries[map->size].value = strdup(value);
    map->size++;
}

void printHashMap(HashMap* map) {
    printf("HashMap Contents:\n");
    for (int i = 0; i < map->size; i++) {
        printf("Key: %s, Value: %s\n", map->entries[i].key, map->entries[i].value);
    }
}


int main() {
    HashMap something;
    something.entries = malloc(INITIAL_CAPACITY * sizeof(Entry));
    something.capacity = INITIAL_CAPACITY;
    something.size = 0;

    insert(&something, "Foo", "Bar");
    insert(&something, "Baz", "Qux");
    insert(&something, "hi", "there");

    // Add any other actions here or print the code for the HashMap
    printHashMap(&something); 
    return 0;
}

See also: