Dynamically sized arrays?

[vgoklani14]

Hi,

How do you create a dynamically sized array in mql4? Is there a *new* construct? I can't even use a variable to define the array size:

int totalEvents = 7;

datetime events[totalEvents];

:(

[bernd]

datetime events[];
ArrayResize(events, totalEvents);

[vgoklani14]

Thanks! Out of curiosity, how expensive is that ArrayResize() function?

[bernd]

vgoklani:
Thanks! Out of curiosity, how expensive is that ArrayResize() function?

Haven't extensively tested it. I think it depends on the size. Once I stumbled upon an EA that (amongst other things) added values to an array after every bar, increasing the array by 1 every time. After a few thousand bars in the strategy tester it became painfully slow and after modifying the EA to increase the array in larger steps of 10% of its size at once it became notably faster again.

[brewmanz]

If you're wanting to keep resizing an array, I would suggest that you re-evaluate your logic, especially of array keeps getting larger.

Array techniques I use are:

- if say varying from 5 to 10, then fix size at 10 but use another variable for size. e.g. double MyArray[10] & int MyArraySize = 7;

- if 'all historical values' then use say double MyHistory[100] and treat it as circular buffer, actually just holding 'last 100 values'
(for circular buffer, either use 'circular index' or else 'shuffle entries & drop oldest' as you add next value )