帮忙看下这段代码是怎么了，谢谢
// The pointer to my tree control.extern CTreeCtrl* pmyTreeCtrl;
UINT i, uCount = pmyTreeCtrl->GetVisibleCount();
HTREEITEM hItem = pmyTreeCtrl->GetFirstVisibleItem();
// Toggle the check state of all the visible items.
for (i=0;i < uCount;i++)
{
ASSERT(hItem != NULL);
pmyTreeCtrl->SetCheck(hItem, !pmyTreeCtrl->GetCheck(hItem));
hItem = pmyTreeCtrl->GetNextVisibleItem(hItem);
}
这段代码为什么提示unresolved external symbol "class CTreeCtrl * pmyTreeCtrl" ？
