free up memory on a double pointer - c++

Question

//char char **p; declared in .h file
size_t bs = 5;
size_t Size = sizeof(obj);
p = (char**)malloc(bs);
for (size_t i = 0; i < bs;i++){p[i] = (char*)malloc(Size);}
for (size_t j = 0; j < bs-1; j ++){p[j] = &(p[j + 1][0]); }
for (size_t i = 0; i < bs; i++){free(p[i]);}
free(p);
my code stalls up when trying to free the last element of p in the for loop. Anyone what i might be doing wrong?
EDIT: I still have the same problem even when changing it to (char*)malloc(bs sizeof(char *));
this still does not work:
size_t bs = 5;
size_t Size = sizeof(obj);
p = (char**)malloc(bs* sizeof(char *));
for (size_t i = 0; i < bs;i++){p[i] = (char*)malloc(Size);}
for (size_t j = 0; j < bs-1; j ++){p[j] = &(p[j + 1][0]); }
for (size_t i = 0; i < bs; i++){free(p[i]);}
free(p);
using new instead of malloc does not solve the issue either
However this code frees up the memory fine.
size_t bs = 5;
size_t Size = sizeof(obj);
p = (char**)malloc(bs* sizeof(char *));
for (size_t i = 0; i < bs;i++){p[i] = (char*)malloc(Size);}
for (size_t i = 0; i < bs; i++){free(p[i]);}
free(p);
so the problem seem to be something with this piece of code
for(size_t j = 0; j < bs-1; j ++){p[j] = &(p[j + 1][0]); }
I want this to be an implicit linked list, anyone know have an idea what i am doing wrong?

Answer 1

You are not allocating enough space for the pointers. Change to
p = malloc(bs * sizeof(char*));

Answer 2

At the first malloc, you don´t need 5 byte, but 5 times a pointer.
p = (char**)malloc(bs * sizeof(char *));

Answer 3

The problem is that you:
allocate an array of 5 pointers
allocate 5 arrays of characters and store them in that first array
move those pointers down in the array, overwriting (and losing) the first pointer and duplicating the last one
attempt to free the 5 pointers in the array.
So on this last step, you free a pointer twice (as the last two entries at p[3] and p[4] are the same), causing undefined behavior.
You say you want "an implicit linked list", implying that you're trying to stuff pointers into the objects (rather than into the top level array, as you are doing), in which case you want something like:
for(size_t j = 0; j < bs-1; j ++) { *(char **)p[j] = p[j + 1]); }
*(char **)p[bs-1] = 0; // null terminate the linked list
this assumes that obj is defined something like:
struct obj {
struct obj *next;
// more fields