I've got a struct x:
struct x {
__s32 array[10];
};
How can I create a pointer to array x->array, if I've got only pointer to stucture?
asked Jan 8, 2017 at 19:17
val - disappointed in SE
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2 Answers
The straightaway method is the commonly used way, as
struct x * ptr = NULL;
//allocation
__s32 * otherPtr = ptr->array; //array name decays to pointer to first member
__s32 (*p) [10] = &(ptr->array); // pointer to whole array.
Otherwise, there's another way, but for specialized cases, quoting C11, chapter §6.7.2.1, Structure and union specifiers
[...] A pointer to a structure object, suitably converted, points to its initial member (or if that member is a bit-field, then to the unit in which it resides), and vice versa. There may be unnamed padding within a structure object, but not at its beginning.
So, in case, the array variable is the first member (or only member, as seen in above example) of the structure, the pointer to the structure variable, suitably converted to proper type, will also point to the beginning of the array member variable.
In this case, you can use a cast of (__s32 (*)[10]).
2 Comments
Stack Exchange Broke The Law
And that is better than &someInstanceOfX->array how?
Sourav Ghosh
@immibis emmm..OK, I did not realize that this was supposed to be a better way, I just thought of an alternate way.
Correct way is
__s32 *pointer = x->array
It is equal to
__s32 *pointer = &(x->array[0])
answered Jan 8, 2017 at 20:19
val - disappointed in SE
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1 Comment
M.M
@SouravGhosh I suspect OP meant "pointer to first element of array"
&(x->array)perhaps?