CODEWITHSUNDEEP
c++arraysrealloc
Saraph
Saraph

Reputation: 1002

Copying content of array to resized array in C++

I've searched through many topics here, but they didn't seem to answer me exactly.

I'm trying to do some dynamic reallocation od arrays in C++. I can't use anything from STL libraries as I need to use this in homework where STL (vectors,...) is explicitly forbidden.

So far, I've tried to elaborate with code like this:

int * items = new int[3]; //my original array I'm about to resize
int * temp = new int[10];
for (int i = 0; i < 3; i++) temp[i] = items[i];

delete [] items;   //is this necessary to delete?
items = new int [10];
for (int i = 0; i < 10; i++) items[i] = temp[i];
delete [] temp;

This seem to work, but what bothers me is the excessive number of iterations. Can't this be done anyhow smarter? Obviously, I'm working with much larger arrays than this. Unfortunately, I have to work with arrays though.

edit: When I try to do items = temp; instead of

for (int i = 0; i < 10; i++) items[i] = temp[i]; and try to std::cout all my elements, I end up with losing first two elements, but valgrind prints them correctly.

Upvotes: 0

Views: 139

Answers (2)

NPE
NPE

Reputation: 500683

Yes, the first delete[] is necessary. Without it, you'd be leaking memory.

As to the code that comes after that first delete[], all of it can be replaced with:

items = temp;

This would make items point to the ten-element array you've just populated:

int * items = new int[3]; //my original array I'm about to resize
int * temp = new int[10];
for (int i = 0; i < 3; i++) temp[i] = items[i];
delete [] items;   //delete the original array before overwriting the pointer
items = temp;

Finally, don't forget to delete[] items; when you are done with the array.

Upvotes: 5

bash.d
bash.d

Reputation: 13207

The containers of the STL were made to ease work like this. It is tedious, but there is not much of a choice, when you need to use C-arrays.

The deletion of 

delete [] items;

is necessary, as when you abandon the reference to the array, which you would do with assigning a new reference in

items = new int [10];

will cause a memory leak, so this is necessary.

Upvotes: 0

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