There is no such thing as std::vector::append in the standard C++ libraries. Though, I assume you might have thought of std::vector::emplace, which is a more complex way of adding data to the vector, offering the possibility of adding your data at a specific point n in the vector, despitestd::vector::push_back, which is not capable of such things. Also the functions std::vector::emplace and std::vector::emplace_back are able to store data structures. The normal std::vector::push_back is not. In order to do that with the C++ 98 function, you need to create another function which is supposed to assign the data to an object, and only after, assigning your already created object to an std::vector of the same type with the object.
PS: std::vector::emplace and std::vector::emplace_back are only accessible from C++ 11.