Pointer to array stored in struct

Question

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?

@SouravGhosh I believe Hermann's point is that a field declared in a structure, that has an array type, is not an array. A field in *a particular instance* of the structure is an array. — user253751, Jan 08 '17 at 19:52
Note that identifiers that begin with a double underscore are "always reserved for any use". See http://stackoverflow.com/questions/1449181/what-does-double-underscore-const-mean-in-c — Andrew Henle, Jan 08 '17 at 20:21

Sourav Ghosh · Answer 1 · 2017-01-08T19:59:39.883

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]).

@immibis emmm..OK, I did not realize that this was supposed to be a better way, I just thought of an _alternate_ way. — Sourav Ghosh, Jan 08 '17 at 19:55

score 1 · Accepted Answer · answered Jan 08 '17 at 20:19

1

Correct way is

__s32 *pointer = x->array

It is equal to

__s32 *pointer = &(x->array[0])

answered Jan 08 '17 at 20:19

val - disappointed in SE

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@SouravGhosh I suspect OP meant "pointer to first element of array" – M.M Jan 09 '17 at 00:04

Pointer to array stored in struct

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