Jason's Notebook

Vectors

2 min read

INFO

A sequence container that organizes data sequentially by index In other programming languages, mostly called Array

  • Organized in the order that they are added
  • Element is retrieved using an index that specifies its place in the sequence
  • Implemented as a Dynamic Array
  • Allows random access1

Constructors

Default Constructor

vector<int> vector1; // construct empty vector
vector1.reserve(5); // reserve 5 element space in vector
vector1.push_back(10); // add the value 10 into vector1

Copy Constructor

vector<int> vector1 = {1, 2, 3};
vector<int> vector2(vector1); // preferred when want to explicit about constructor call
vector<int> vector3 = vector1; // also calls the copy constructor

Initializer list

// both of the following syntax is valid
vector<int> vector1{3, 4, 5, 6, 7};
vector<int> vector2 = {3, 5, 7, 9};

Range Constructor

// creates a new vector that has all elements from index2 to the end of the vector in vector1
auto iter = vector1.begin() + 2;
vector<int> vector2(iter, vector1.end());
 
int arr[] = {10, 11, 12, 13};
vector<int> vector3(arr, arr + 3); // contains {10, 11, 12};

Size, Capacity, and Efficiency Issues

  • Vector has capacity(correspond to how many memory is allocated)
  • Size: denotes the number of elements
  • Vectors grow automatically
  • vector::push_back() can be inefficient
    • If no more space to fit new element → new dynamic array formed with larger capacity → all elements are copied into the new dynamic array
  • Capacity of vector should be set using default constructor
vector<int> vector1;
vector1.reserve(10);

Inserting and Replacing Element

Single Element

iterator insert(const_iterator position, const value_type& val);

N Elements of the Same Value

iterator insert(const_iterator position, size_t n, const value_type& val);

Initializer List

iterator insert(const_iterator position, initializer_list<value_type> list);

Initialize Vector with 0’s

Overloaded Constructor

vector<int> vector1(8); // 0, 0, 0, 0, 0, 0, 0, 0

Resize Member Function

vector1.resize(10); // 1, 2, 3, 4, 5, 6, 7, 0, 0, 0

Member Functions

  • vector::push_back(const T& val): Add Element val at the end
  • vector::front(): Access first element
  • vector::back(): Access last element
  • vector::erase(iterator position): Erase element at position
  • vector::insert(iterator position, const T& value): Insert value at position
  • vector::pop_back(): delete last element

Footnotes

  1. The ability to retrieve or modify any element in a Data Structure directly, without needing to traverse other elements ↩

Graph View

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