How to get the pointer to certain clock element by its index

Asked Nov 08 '19 at 14:56

Active Nov 08 '19 at 15:05

Viewed 64 times

I have 2 structures:

struct page
{
    VA adress;
    void* data;
    size_t filled_bytes;
};

struct mmemory
{
    int pages_count;
    int page_size;
    int pages_allocated;
    int pages_filled;
    struct page* table;
} *MMEM;

Then I've made mallocs:

MMEM = malloc(sizeof(struct mmemory));
MMEM->table = malloc(sizeof(struct page*) * n);

//in for loop
struct page* new_page = malloc(sizeof(struct page));
new_page->data = malloc(MMEM->page_size);
MMEM->table[MMEM->pages_allocated++] = *new_page;

I want to get the pointer to certain element of MMEM->table[0].data by index 0, for example. According to this question I should cast data to char* and than get it element by index. I've tryed:

&MMEM->table[MMEM->pages_filled].data[0] -- Expression must be a pointer to a complete object type using simple pointer arithmetic

&(char*)(MMEM->table[MMEM->pages_filled].data[0]) -- the same

edited Nov 08 '19 at 15:05

asked Nov 08 '19 at 14:56

Pavel Antspovich

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4

Did you intend to write `MMEM = malloc(sizeof(struct page));` instead of `MMEM = malloc(sizeof(struct mmemory));` ? – Sander De Dycker Nov 08 '19 at 14:59
3

Likewise, for a declaration `struct page* table;` then `MMEM->table = malloc(sizeof(struct page*) * n);` should be `MMEM->table = malloc(sizeof(struct page) * n);` (note the removal of one star). – Adrian Mole Nov 08 '19 at 15:01
@SanderDeDycker, my bad, thanks – Pavel Antspovich Nov 08 '19 at 15:06
1

data is a void *, so & ... .data[0] is meaningless. If you simply want what data points to; the MMEM->table[MMEM->pages_filled].data is sufficient; if you want an alias of 'data' (a pointer to a pointer), then &MMEM->table[MMEM->pages_filled].data. – mevets Nov 08 '19 at 15:06
@mevets, how could I get the pointer to data[0] element? – Pavel Antspovich Nov 08 '19 at 15:08
`MMEM->page_size` is not initialized. – Paul Ogilvie Nov 08 '19 at 15:12
@mevets, I'vу created alias and get pointer by it. Thanks! – Pavel Antspovich Nov 08 '19 at 15:12

How to get the pointer to certain clock element by its index

0 Answers0