向量构造函数的内存分配，用于常量迭代器，seg错误

Question

I am having troubles figuring out how to allocate space for this constructor. It is supposed to construct a Vector with elements from another Vector between start and end.

template <class T> Vector<T>::Vector(const_iterator start, const_iterator finish)
{
    array = new T[2 * capacity()];

    for( ; start != finish; start++ ){
        push_back(*start);
    }
}

I have been trying to debug this, but cannot figure it out. push_back looks like so:

template <class T> void Vector<T>::push_back(const T & val)
{
    if (size() == capacity()) {
        reserve (2 * capacity() + 1);
    }

    array[ theSize++ ] = val;
}

Which calls reserve..

template <class T> void Vector<T>::reserve(int newCapacity)
{
    if (newCapacity < size()) {
        return;
    }

    T * array_copy = array;

    array = new T [newCapacity];
    for (int i = 0; i < size(); i++) {
        array[i] = array_copy[i];
    }

    theCapacity = newCapacity;

    delete [] array_copy;
}

So, to narrow the question down:

Why is the segmentation fault happening?

Answer 1

You didn't initialize size() and capacity() in the constructor. The push_back() called in constructor may be affected by the randomly initialized values.