Vectors

• This is chapter 18, the beginning
• reference.
• This is your new favorite C++ array. Use it unless forbidden.
• He provides a list of requirements to use these containers on 629-630
  • These are things you should implement in your classes anyway.
  • We will discuss these in detail in chapter 7-10
• The vector class implements a dynamic array.
  • Sequential container
  • Grows and shrinks as needed.
  • Constant time random access - what does that mean?
  • Plus access to the underlying storage if needed
    • For libraries from C for example.
    • Not for normal access.
  • constant insert/delete at the end.
  • O(n) insert/delete anywhere else - but as measured from the end.
• #include <vector>
• Declaration and initialization
  • It is a template so we need to specify the type.
    • vector <type> identifier
    • vector <int> values;
    • vector <BeetleT> bugs;
  • A using statement is sometime helpful here
    • using BugArrayT = vector < BeetleT>;
• There are several ways to initialize a vector
  • vector<type>id build an empty vector.
  • vector<type>id(size_t,[{values}]) builds a vector of size initializing to the given values.
  • There are others. The cppreference page has 10 different versions.
• Declaring a multi dimensional vector
  • vector<vector<int>>id(size,vector<int>(size,value))
  • Any deeper than this I would start to use using or switch to a multidimensional array library.
• The member functions to know:
  • push_back, pop_back: add or remove the last element.
  • size() or length() : return the number of elements.
  • [i] or .at(i) : access element i, 0 ≤ i < size()
  • front(), back(): access the first/last element.
  • True assignment (=)
  • data(): returns a pointer the the underlying storage, for use with c routines.
• see vecTest.cpp