What does the array subscripting operator ([ ]) do to an array?

Question

I'm wondering what the array subscripting operator ([]) do to objects

From this question and this question, I learnt that the [] operator takes an address of an object, adds whatever it is in between the brackets to the object and finally dereferences the sum to obtain an address. However, in array declarations, eg.

int iarr[] = {1,2};
int iarr2[2] = {1,2};

The [] operator doesn't seem to be adding the value in the brackets to the operand, especially in the second example. Instead, it seems to be giving the object the ability to store arrays.

Also, my wild guess is that in int arr2[2] = {1,2}, arr[2] will allocate memory for two ints. Is that true?

As a summary:

What does the [] operator do to its operand during declaration? Does it just give the object the ability to store arrays or does it allocated memory for the array instead?

The meaning of [] depends on the context but in your case it's not an operator. It's the syntax do declare or initialize an array. — Thomas Sablik
– Thomas Sablik, Commented Oct 14, 2019 at 11:35
Remember that C++ uses a Context-sensitive grammar. The same symbol often means different things in different contexts. — Jesper Juhl
– Jesper Juhl, Commented Oct 14, 2019 at 12:33

molbdnilo · Accepted Answer · 2019-10-14 11:36:02Z

6

[] is an operator only when applied to an expression.
(The same principle holds for & and *.)

In a declaration, it's part of the type and doesn't really "do" anything other than specify that the declared variable is an array.

answered Oct 14, 2019 at 11:36

molbdnilo

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pcarter · Accepted Answer · 2019-10-14 11:39:16Z

2

You are confusing the [] operator and the syntax for declaring an array.

int iarr2[2] = {1,2};

is declaring an array named iarr2 of 2 integers and then initializing the elements of the array to 1 and 2. It is not applying the [] operator.

answered Oct 14, 2019 at 11:39

pcarter

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Marek R · Accepted Answer · 2019-10-14 11:49:39Z

1

This:

int iarr[] = {1,2};

Means define an array which size will mach number of elements in initialization list.

On other hand:

 int iarr2[2] = {1,2};

Means define an two element array and initialize it to 1 and 2

You can do also:

 int iarr2[4] = {1,2};

Means define an four element array and initialize first two elements to 1 and 2. Remaining elements are initialized to: 0

answered Oct 14, 2019 at 11:49

Marek R

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