减少数组的大小

Question

I had an array with a lot of numbers and I had to "remove" some of them so I decided to put zeros instead which I could just ignore latter on and so I got this:

0033033055000022220440044000

But now I realize I need to add the n-1 to the original size, for example I have 5 so I need to add the number before it which is 3 , the problem now is I don't need the zeros.

Therefore, is there a way to reduce an array in size/remove unneeded indexes or would it just simpler to write a function which would loop until it found an integer?

Answer 1

std::vector<int> values;
values.erase(std::remove(values.begin(), values.end(), 0));
values.shrink_to_fit();

std::remove puts all elements which match the given value (0 in this case) in the end of the vector, and returns an iterator to the start of the removed elements. Erase then takes this iterator and removes all subsequent values from the vector. shrink_to_fit then attempts to reallocate the vector with a smaller amount of memory, taking into account the reduced number of elements. Unless you are removing thousands of elements, it's not really worth shrinking the vector.

Answer 2

What you are trying to accomplish is possible. By using malloc() and realloc() you can dynamically set the size of the array you're using, thus allowing you to grow/shrink arrays as you need to.

It's complicated, and requires careful pointer management. If that is the path you'd like to go down, then there are several tutorials online for things like that. This was the first thing I found with a google search, and seems to give the basic idea behind how to do what you want to do.

That being said, Don't do that. the standard library (STD) has several different tools to store data that would be better suited to the task. Vectors are a classic choice and work almost exactly like arrays, but they are generally poor when you are removing items from the middle of them. Lists are REALLY good at deleting items in the middle of them, but traversing them can be a pain, as you have to start at the beginning and work your way through (you can't access things in the middle willy nilly at will.) Choose whichever of these suit your needs better, and use those. It will simplify your life.