array initialisation syntax

Question

I've just come across this in code and I don't understand what it's doing, or how it's doing what it's doing

pos[iter](1) += 12.0f / 900.0f;

does the (1) initialise the array value at position iter to 1, then add (12.0f / 900.0f) to it? I can't believe it is as it's being used in a loop to set the position of debug text, each loop sets the next line below to a high y value (lower point on screen). iter can be 0 or 1 depending on what list the debug text is in.

I would understand if it were a static operation.

You must include the declaration of `pos` in order to understand this line. It could be a container of function pointers, e.g. — Brian Cain, Mar 26 '13 at 13:41
The important thing here is that it's not some strange syntax you've never seen before. It's just accessing an array and then calling a function. — Joseph Mansfield, Mar 26 '13 at 13:47
Does this code compile? Is it an example from a book? The `(1)` could be a cross-reference to some description, and not meant to be part of the code at all. — Peter Wood, Mar 26 '13 at 13:49

score 5 · Accepted Answer · edited May 23 '17 at 12:11

pos[iter](1) += 12.0f / 900.0f;

pos can be an array, map, or an object of a class with an overloaded operator[]. pos[iter] returns an object (could be a function pointer, lambda or a class with an overloaded operator()) and calls it with a parameter of 1. The function call most likely returns a reference to the returned object as you can mutate its value using +=.

So to make it clear, (1) is not accessing the 2nd element of anything. It's simply a call to a function or method with that argument. The method returns some object that has a suitable overload of operator += (could be a scalar or an actual class).

It could also be a pointer to a function pointer... just too many possibilities... — PlasmaHH, Mar 26 '13 at 13:45

array initialisation syntax

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