Can you resize a C++ array after initialization? [duplicate]

Answer 1

If you want to know why your first idea compiled but didn't seem to work:

When you omit braces in an if-statement:

if ((n % 2) != 0) int farray[halfelements + 1];

it's just the same as if you'd used them:

if ((n % 2) != 0) {
  int farray[halfelements + 1];
}

So it is making an 'farray' of the correct size -- and then it immediately goes out of scope and is gone, and you're left with only the original one.

Answer 2

If you want to resize an array, you probably want to use a vector, which can be resized automatically.

Answer 3

You can use the [] operator with a vector the same way you would in an array. You could implement this with a vector something like this (if you wanted to use more vector methods):

#include <vector>

const int halfelements = originalarray.size()/2; //use size to get size
vector <int> farray(halfelements);
vector <int> farray(halfelements);

for (int i = 0; i < halfelements; i++) {
    farray.push_back(originalarray[i]); //adds element at i to the end of vector
}

for (int i = halfelements, x = 0; i < (halfelements * 2); i++, x++) {
    sarray.push_back(originalarray[i]);
}

You can also use .at(index) to add bounds checking to the vector access.

Answer 4

C++ arrays are fixed in size.

If you need a "resizable array", you'll want to use std::vector instead of an array.

Answer 5

I would also recommend std::vector. However if you are stuck with an array you can always malloc the memory and then realloc if you need to make the array larger.

Do a search here on SO, there is information about malloc and realloc.

Answer 6

My advice is even stronger: use std::vector<> (et. al.) unless you have a very good reason to use a C-style array. Since you're learning C++, I doubt you have such a reason: use std::vector<>.