Question

I have a dynamically allocated array :

myRectangle lastRectanglesArray = new myRectangle[lastMaxLabel];

I would like to loop through all elements in this array and remove these that will meet my condition (e.g. too big rectangle).

I have been thinking that I can loop through this array and get the number of elements that would satisfy my condition and then allocate a new array. But how can I ‘transfer’ these ‘wanted’ elements into my new array ?

Just for the record: I cannot use STL containers.

Answer 1

myRectangle * lastRectanglesArray = new myRectangle[lastMaxLabel];
// initialize the entries in the lastRectanglesArray

// create a temporary array which contains info about each individual
// entry. namely, it only holds info about whether the entry should
// be kept, or deleted.
// we also use the 'entries' value, which is the number of entries
// in the new array
bool * entriesToKeep = new bool[lastMaxLabel];
int entries = 0;

// check each entry, and mark whether it should be kept or deleted
for (int i = 0; i != lastMaxLabel; ++i) {
    // check whether the entry should be kept or deleted...
    // here, i just put a function with signature like:
    // bool shouldKeepRectangle(const myRectangle &);
    entriesToKeep[i] = shouldKeepRectangle(lastRectanglesArray[i]);
    if (entriesToKeep[i]) ++entries;
}

// create a new array that will contain the entries that should be kept
myRectangle * rectanglesArray = new myRectangle[entries];

// assign the entries in the new array
for (int i = 0, j = 0; i != lastMaxLabel && j != entries; ++i) {
    if (entriesToKeep[i])
        rectanglesArray[j++] = lastRectanglesArray[i];
}

// free the memory held by the temp array
delete [] entriesToKeep;

// if the old array is not needed anymore, delete it
delete [] lastRectanglesArray;

// and here you have rectanglesArray, a brand new array that contains
// only the elements that you need.