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Comments on 2D-array pointer as a struct member

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2D-array pointer as a struct member

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I have an array of struct:

static struct basket baskets[MAX_ITEMLEN + 1];

struct basket {
  char *items;      // malloc(itemlen * itemcount)
  int itemcount;
};

char *items does all I need to do with some pointer-gymnastics, but at times it gets a little ugly.

I would prefer a 2D-array pointer allowing items[item_index][char_index] navigation by default, but all my attempts to get a 2D-array pointer as struct member have failed miserably.

If it is indeed possible: how?

Details (in case relevant):

#1 Specs:

#define MAX_ITEMLEN 20  
#define MAX_ITEMCOUNT 16000

#2 itemcount(s) & the char content of each item are not known at compile-time but are derived at start-up by parsing two user-provided .txt files

#3 The code will not interrogate baskets[x] having itemcount == 0

#4 *items is initialised: |←item_chars→|←item_chars→| ...itemcount times ...with no delimiters ('\0' or otherwise)

#5 After initialsation, basket[] is invariant until exit()

c array
posted 2 days ago
17h ago
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wasIzy‭
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1 comment thread

Are the data strings? (3 comments)
Are the data strings?
Lundin‭ wrote 1 day ago
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In case the data is strings, an array of pointers char** is often the most convenient since it is flexible and memory efficient, but at the cost of execution speed. If the data is something else, then the flexibility of using a char** is probably not worth it.

wasIzy‭ wrote about 20 hours ago
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Data are values that fit comfortably in a char, NOT strings. They may match a "dictionary word" in some language, but are NEVER used in any string-like context (string.h, printf...%s, etc).

Execution speed is important: the code will access baskets[] millions of times in a run, how many millions depends on the user-provided "problem definition".

BTW your SO self-answered question on correctly declaring 2D-arrays is one of the very few bookmarks tagged GOLD in my browser. If only it covered struct...

wasizy

Lundin‭ wrote about 9 hours ago
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wasIzy‭ The char* member isn't ideal either for performance reasons, since it will point at data allocated outside the struct array. Ideally the struct array will be allocated on the heap too, along with the pointed-at data. But if you want this to be truly flexible and realloc:able, you'll probably have to accept that the data is stored elsewhere.