Implementing a Vector in C: A Practical Guide

While C does not natively support dynamic arrays like higher-level languages such as Python, it is indeed possible to implement a vector-like structure using a combination of structures and dynamic memory allocation. This article will guide you through creating a simple vector implementation in C, providing a detailed explanation and example code.

Introduction to Vector Implementation in C

Dynamic arrays in C are typically implemented using a combination of a structure to hold the array pointer and a size counter. While C lacks built-in support for vectors, it offers means to dynamically allocate memory and resize arrays as needed. This article will demonstrate how to create a basic vector implementation in C.

Structure Definition

A vector structure in C consists of a pointer to the element array, the current size of the vector, and the capacity of the vector (i.e., the maximum number of elements that can be stored).

typedef struct {
    int* data           // Pointer to the array of elements
    size_t size         // Current number of elements
    size_t capacity     // Maximum number of elements that can be stored
} Vector;

Creating a Vector

The create_vector function initializes a new vector with a specified initial capacity.

Code Example

Vector create_vector(size_t initial_capacity) {
    Vector vec  malloc(sizeof(Vector));
    vec-data  malloc(initial_capacity * sizeof(int));
    vec-size  0;
    vec-capacity  initial_capacity;
    return vec;
}

Adding Elements to the Vector

The vector_push_back function adds elements to the vector. If the current size reaches the capacity, it doubles the capacity and reallocates memory.

Code Example

void vector_push_back(Vector vec, int value) {
    if (vec-size  vec-capacity) {
        // Resize the vector if necessary
        vec-capacity  vec-capacity * 2;
        vec-data  realloc(vec-data, vec-capacity * sizeof(int));
    }
    vec-data[vec-size]  value;
    vec-size  ;
}

Accessing Elements in the Vector

The vector_get function retrieves elements from the vector, checking for out-of-bounds access.

Code Example

int vector_get(Vector vec, size_t index) {
    if (index  vec-size) {
        fprintf(stderr, "Error: Out of bounds access
");
        exit(EXIT_FAILURE);
    }
    return vec-data[index];
}

Memory Management

The free_vector function cleans up the allocated memory for the vector.

Code Example

void free_vector(Vector vec) {
    free(vec-data);
    free(vec);
}

Usage

You can compile and run the following code using a C compiler. It demonstrates creating a vector, adding elements, accessing them, and cleaning up resources.

Code Example

#include stdio.h
#include stdlib.h
typedef struct {
    int* data           // Pointer to the array of elements
    size_t size         // Current number of elements
    size_t capacity     // Maximum number of elements that can be stored
} Vector;
Vector create_vector(size_t initial_capacity) {
    Vector vec  malloc(sizeof(Vector));
    vec-data  malloc(initial_capacity * sizeof(int));
    vec-size  0;
    vec-capacity  initial_capacity;
    return vec;
}
void vector_push_back(Vector vec, int value) {
    if (vec-size  vec-capacity) {
        vec-capacity  vec-capacity * 2;
        vec-data  realloc(vec-data, vec-capacity * sizeof(int));
    }
    vec-data[vec-size]  value;
    vec-size  ;
}
int vector_get(Vector vec, size_t index) {
    if (index  vec-size) {
        fprintf(stderr, "Error: Out of bounds access
");
        exit(EXIT_FAILURE);
    }
    return vec-data[index];
}
void free_vector(Vector vec) {
    free(vec-data);
    free(vec);
}
int main() {
    Vector vec  create_vector(4); // Create a vector with an initial capacity of 4
    // Add elements to the vector
    for (int i  0; i  10; i  ) {
        vector_push_back(vec, i);
    }
    // Print elements in the vector
    for (size_t i  0; i  vec-size; i  ) {
        printf("%d ", vector_get(vec, i));
    }
    printf("
");
    // Free the vector
    free_vector(vec);
    return 0;
}

In this simple implementation, we have demonstrated the basic functionality of a vector in C. This example can be extended with additional functionality like removing elements, inserting at specific positions, and more utility functions.