C / C++ / MFC

vector <CMyTrailer> m_Item;
vector <CMyTrailer> m_MFG;

...fill...

m_Item.insert( m_Item.end(), m_MFG.begin(), m_MFG.end());

std::vector<int> v1;
std::vector<int> v2;
 
std::copy(v1.begin(), v1.end(), std::back_inserter(v2));

void CTrlMasterDlg::AddVecItem(const ITEM& vec) {
    std::copy(vec.begin(), vec.end(), std::back_insertor(m_Item));
}

void CTrlMasterDlg::AddVecItem(const ITEM& vec) {
    for (ITEM::iterator it = vec.begin(); it != vec.end(); it++) {
        m_Item.push_back(*it);
    }
}

ITEM::iterator it = vec.begin();

(*it).m_csData;
 
or even better
 
it->m_csData;