free struct of unions in c -

i have dynamically allocated vector of special struct, , trying free software crashes

the structure :

typedef struct {     type_e type;     union {         char m_char;         int m_int;         // more types (non of them pointer)     } my_data; } data_t; 

where type enum contain possible data types.

i allocate , initialize vector follows

void vector(data_t **vec, uint32_t start_element, uint32_t end_element, type_e type) {     uint32_t i;     data_t  *vec_ptr;      *vec=(data_t *)malloc((size_t) ((end_element-start_element+1) * sizeof(data_t)));      vec_ptr = *vec;      if (!vec_ptr)      {         // write error      }      (i =start_element; <= end_element + 1; i++)     {         vec_ptr->type = type;         switch (type)         {         case uint32: vec_ptr->my_data.m_int = 0; break;         // more possible cases         default:             break;         }         (vec_ptr)++;     } } 

i call function follows

data_t *lvector = null; vector(&lvector,0,10,int32) 

but when try free allocated memory follows,

free (lvector+start_element-1); 

i tried

free (lvector+start_element); 

and

free (lvector); 

were start_element = 0 (in case)

but in cases, crash. doing wrong ?

this parameter says array of pointers type 'data_t'

data_t **vec, 

however, line:

*vec=(data_t *)malloc((size_t) ((end_element-start_element+1) * sizeof(data_t))); 

allocates memory array of 'data_t' not array of pointers 'data_t'

in c, not cast returned value malloc

the parameter malloc() automatically 'size_t' casting 'size_t' clutters code

---

this line:

for (i =start_element; <= end_element + 1; i++) 

iterates on array index 0 index 11 however, valid index 0 10 c array indexs start 0 , end @ sizeof(array) -1

---

this line:

(*vec)->type = type; 

is expecting 'vec' array of pointers struct. but, mentioned earlier, not

---

this line:

*vec  = *vec + sizeof(data_t); 

is stepping through array of struct however, looses pointer malloc'd memory, resulting in memory leak because pointer malloc'd memory lost cannot passed free()

---

this line:

*vec = *vec - ((end_element-start_element+1) * sizeof(data_t)); 

doesn't quite work, because prior 'for' statement iterates 1 many times.

strongly suggest indexing off 'vec' rather changing vec contents. i.e. vec[i]