Simple Vector in C

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

struct vector {
    void (*val_free)(void *);
    uintptr_t *data;
    int cap;
    int len;
};

/*********************************************************************
 *                                                                   *
 *                    constructor / destructor                       *
 *                                                                   *
 *********************************************************************/

/*************
 * vec_alloc *
 *************/

struct vector *
vec_alloc(int cap, void (*val_free)(void *))
{
    struct vector *vec;
    uintptr_t *data;

    vec = malloc(sizeof(struct vector));
    data = malloc(cap * sizeof(uintptr_t));

    vec->val_free = val_free;
    vec->data = data;
    vec->cap = cap;
    vec->len = 0;

    return vec;
}

/************
 * vec_free *
 ************/

void
vec_free(struct vector *vec)
{
    if (vec->val_free) {
        for (int i = 0; i < vec->len; i++) {
            if (vec->data[i])
                vec->val_free((void *)vec->data[i]);
        }
    }

    free(vec->data);
    free(vec);
}

/*********************************************************************
 *                                                                   *
 *                            insertion                              *
 *                                                                   *
 *********************************************************************/

/************
 * vec_push *
 ************/

/* pushes item to the back of the vector */

void
vec_push(struct vector *vec, uintptr_t src)
{
    if (vec->len == vec->cap)
        resize(vec, vec->cap * 2);

    vec->len++;
    vec->data[vec->len - 1] = src;
}

/*********************************************************************
 *                                                                   *
 *                             deletion                              *
 *                                                                   *
 *********************************************************************/

/***********
 * vec_pop *
 ***********/

/* removes the last item in the vector, copies it to dst */

uintptr_t
vec_pop(struct vector *vec)
{
    uintptr_t res;

    if (vec->len < 3 * vec->cap / 4)
        resize(vec, 3 * vec->cap / 4);

    res = vec->data[vec->len - 1];

    vec->len--;

    return res;
}

/*********************************************************************
 *                                                                   *
 *                            retrieval                              *
 *                                                                   *
 *********************************************************************/

/************
 * vec_peek *
 ************/

/* copies the item at an index to dst */

uintptr_t
vec_peek(struct vector *vec)
{
    if (vec->len > 0)
        return vec->data[vec->len - 1];
    return 0;
}