dereferencing through a vector error

Question

For my constructor, I input a integer vector, and within the constructor, I set another vector of type bool called theSet. From the input vector, I check every element to see if its between 0 and 20, if true then element of theSet is true.

However I'm having problems with my implementation of dereferencing theSet vector.

class Set
{
public:
    Set(vector<int> &);
    bool IsMember(int);

private:
    vector<bool> theSet;

}

bool Set::IsMember(int x)
{
    if ((x >= 0) && (x <= 20))
        return true;
    else
        return false; 
}


Set::Set(vector<int> &v)
{
    int length = v.size();
    theSet.reserve(length);

    bool check;

    int p = 0;
    for (int i = 0; i < length; i++)
    {
        theSet[i] = IsMember(v[i]);
    }
}

Answer 1

Use theSet.resize() instead of theSet.reserve() and it'll probably work. Please try. With reserve() you are just pre-allocating memory for inserts, but the memory itself is unitialized, resp. there are no real elements yet. When you try to modify the values within your loop you'll request a reference to the value at position i, but there's no element that could be modified, hence the error.