Generic dynamic array

Here is the interface of my generic dynamic array;

/* dynamic array interface */

#ifndef DA_HEADER
#define DA_HEADER

#include  /* size_t */

/* creates a new dynamic array, with each element of "size" bytes */
void *danew(size_t unitsize);

/* returns pointer to element after the last element */
void *daend(void *arr);

/* appends new element after last element 
   return pointer to array head
*/
void *daappend(void *arr, const void *elem);

/*
    removes the last element and returns a pointer to it or null if empty
*/
void *dapop(void *arr);

/*
  frees the array
*/
void dafree(void *arr);

#endif /* DA_HEADER */

and this is the implementation of my generic dynamic array:

```
/ dynamic array implementation /

#include / memcpy /
#include / free /
#include "xalloc.h" / xmalloc, xrealloc /

struct dynamic_array {
size_t cap;
size_t len;
size_t unitsize;
char data[1];
};

#define DATAOFFSET ((unsigned long)(((struct dynamic_array*)0)->data))
#define DA_STRUCT(DATAPTR) (struct dynamic_array )((char )DATAPTR-DATAOFFSET)

void *danew(size_t unitsize)
{
/ -1 because we already have one byte in struct /
struct dynamic_array *da = xmalloc(sizeof(struct dynamic_array) +
unitsize - 1);

da->cap = 1;
da->len = 0;
da->unitsize = unitsize;

return &(da->data);
}

static __inline struct dynamic_array __dagrow(struct dynamic_array da,
size_t size)
{
while(size > da->cap)
da->cap = 2*da->cap;

/ -1 because we already have one byte in sizeof(struct) /
return xrealloc(da, sizeof(struct dynamic_array) + da->unitsize*da->cap
- 1);
}

void daappend(void arr, const void *elem)
{
struct dynamic_array *da = DA_STRUCT(arr);
da = __dagrow(da, da->len + 1);
memc

-
naming da* + all lower case makes it hard to parse the difference between the prefix and the name of the function, instead either pick da_snake_case or daCamelCase.

-
returning void* is not ideal instead create a opaque (incomplete) struct and just let the use pass pointers to that struct around:

struct DynamicArray;

DynamicArray* danew(size_t unitsize);

StackExchange Code Review Q#85495, answer score: 3