If I have an array and all I have is an upper limit on how big the array can get, and if the number of elements that get added can be considerably smaller than this limit, is it always the right choice to declare a pointer and just reallocate extra memory whenever the array grows?
For instance, instead of declaring int a[max] I can declare a pointer int *a and than just realloc when I add elements. This would save memory. Is there any drawback to doing this?
Last edited by zaphod; 10-15-2014 at 12:43 AM.
The drawback is that it tends to be expensive (as in there's a cost in terms of time that might not be negligible) to call realloc for each new element. One way to mitigate this is to separate the notion of the number of elements in use from its capacity. That is, you start with some initial capacity, after which you can increase the capacity of the dynamic array by a factor (e.g., doubling it) when necessary (i.e., when the number of elements in use will exceed the capacity). This way, you trade having no unused space for fewer calls to realloc.
However, when the dynamic array's capacity gets too large, it may be the case that you should increase the capacity by a constant amount instead of a constant factor, or risk allocation failure or simply too many unused elements. So, there is another drawback here in that your scheme for managing the capacity of an dynamic array could become far more complicated than if you just had a large fixed size array.
Oh, and of course, you must remember to free what you malloc/realloc.
Look up a C++ Reference and learn How To Ask Questions The Smart WayOriginally Posted by Bjarne Stroustrup (2000-10-14)
