learning c lol

vec.c

/* Vec */

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

#define LAST_OF(array, length) array[length-1]

size_t get_capacity(size_t length)
{
    size_t capacity = 1;

    while (capacity < length)
        capacity *= 2;
    
    return capacity;
}

typedef struct Vec
{
    long long *ptr;
    size_t length;
    size_t capacity;
} Vec;

long long vec_get(Vec *self, size_t index)
{
    if (index >= self->length)
    {   
        // This is terrible error handling but I don't know how to do it properly lol
        fprintf(stderr, "Error: vec_get: index %lu is out of bounds", index);
        exit(-1);
    }

    return self->ptr[index];
}

_Bool vec_needs_growing(Vec *self)
{
    return self->length + 1 >= self->capacity;
}

void vec_grow(Vec *self)
{
    size_t new_length = self->length + 1;
    size_t new_capacity = get_capacity(self->length);

    long long *new_ptr = malloc(sizeof(long long) * new_capacity);

    for (unsigned int i = 0; i < self->length; i++)
        new_ptr[i] = self->ptr[i];

    free(self->ptr);

    self->ptr = new_ptr;
    self->length = new_length;
    self->capacity = new_capacity;
}

void vec_print(Vec *self)
{
    printf("[");

    for (unsigned int i = 0 ; i < self->length; i++)
    {
        if (i > 0)
            printf(", ");

        printf("%lld", self->ptr[i]);
    }

    printf("]\n");
}

void vec_append(Vec *self, long long value)
{
    if (vec_needs_growing(self))
        vec_grow(self);
    else
        self->length++;

    LAST_OF(self->ptr, self->length) = value;
}

long long vec_pop(Vec *self)
{
    long long value = LAST_OF(self->ptr, self->length);

    self->length--;

    return value;
}

Vec* vec_new(size_t argc, ...)
{
    va_list argv;
    va_start(argv, argc);

    size_t capacity = get_capacity(argc);

    Vec *v = malloc(sizeof(Vec));
    v->ptr = malloc(sizeof(long long) * capacity);
    v->length = argc;
    v->capacity = capacity;
    
    for (unsigned int i = 0; i < argc; i++)
        v->ptr[i] = va_arg(argv, long long);

    return v;
}

int main(void)
{
    Vec *v = vec_new(3, 86, 41, 237);

    printf("length: %lu, capacity: %lu\n", v->length, v->capacity);
    vec_print(v);
    printf("2nd element: %llu\n\n", vec_get(v, 1));
    
    vec_append(v, 19);
    printf("length: %lu, capacity: %lu\n", v->length, v->capacity);
    vec_print(v);
    printf("4th element: %llu\n\n", vec_get(v, 3));

    vec_pop(v);
    printf("length: %lu, capacity: %lu\n", v->length, v->capacity);
    vec_print(v);
    
    free(v);
}