Changing the reserve memory of C++ vector

if(count + 1 > m_listItems.capacity())
     m_listItems.reserve(count + 100);

m_listItems.clear();

vector<Item>(m_listItems).swap(m_listItems);

vector<Item>().swap(m_listItems);

std::vector<foo> v(1000); // Create a vector with capacity for 1000 elements

std::vector< int > v;
// ... fill v with stuff...
std::vector< int >().swap( v );

vector< int > tmp;
old.swap( tmp );