Preprocessor checks for array members

Question

These 2 arrays are being modified a lot in the source code, that is why I want the preprocessor to count the number of members in the array. Is it also possible to have the gcc preprocessor check that array a ends in NULL and array b ends in 0?

static const char *a[] = { "string1", "string2", NULL };

static const int b[] = { 10, 20, 0 };

The preprocessor doesn't know anything about arrays... So I don't think it can check anything like than. You should clarify what you are trying to do. — hivert, Jul 26 '13 at 17:16
No, you can't do this using the preprocessor, you have to pay attention. Or even better, require storing the length of the array explicitly. — , Jul 26 '13 at 17:20

score 2 · Accepted Answer · edited Jul 26 '13 at 17:43

2

There are a few things the preprocessor can do for you, but not quite what you describe. You can determine the number of elements in the array using a macro:

#define COUNTOF(arr)  (sizeof(arr) / sizeof(*(arr)))

then somewhere in a function you can use assert() to test the values:

#include <assert.h>
...
... in some function
...

assert(a[COUNTOF(a) - 1] == NULL);
assert(b[COUNTOF(b) - 1] == 0);

or something to that effect.

edited Jul 26 '13 at 17:43

Jonathan Leffler

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answered Jul 26 '13 at 17:35

andy mango

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Thank you. I did not know it could be done with 2 dimensional char arrays. – elaine Jul 26 '13 at 19:36
@elaine not sure what you mean by "2 dimensional char arrays". In this case "a" is an array of pointers to characters. – andy mango Jul 26 '13 at 20:00

Preprocessor checks for array members

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