pair[¹]

Pair is used to combine together two values that may be different in type.

• 初始化需要声明类型 pair<int, int> 。或者使用make_pari()函数，就可以使用auto了
• 初始化可以是：(下面没声明类型，没法跑的)

  pair  g1;         //default
  pair  g2(1, 'a');  //initialized,  different data type
  pair  g3(1, 10);   //initialized,  same data type
  pair  g4(g3);    //copy of g3
  

• tie(int &, int &) = pair1; : unpack values, like python, but have to use tie
  • 不能嵌套
• 操作符比较：
  • == ：两个都要比
  • != : 两个都要比
  • <=,>=: 两个都要比
• swap

tuple

A tuple is an object that can hold a number of elements. The elements can be of different data types. The elements of tuples are initialized as arguments in order in which they will be accessed.

• get

  // Use of get() to change values of tuple
  get<0>(geek) = 'b';
  get<2>(geek) =  20.5;
  

• make_tuple
• tuple_size

  tuple <char,int,float> geek(20,'g',17.5);
  // Use of size to find tuple_size of tuple
  cout << tuple_size<decltype(geek)>::value << endl;
  

• swap
• tie
• tuple_cat

  // Concatenating 2 tuples to return a new tuple
  auto tup3 = tuple_cat(tup1,tup2);
  

Vecotr

Vectors are the same as dynamic arrays with the ability to resize itself automatically when an element is inserted or deleted, with their storage being handled automatically by the container. Vector elements are placed in contiguous storage so that they can be accessed and traversed using iterators.

• begin:
• end:

  vector<int> myvector{ 1, 2, 3, 4, 5 };
   
  // using end() to print vector
  for (auto it = myvector.begin(); it != myvector.end(); ++it)
      cout << ' ' << *it;
  

• rbegin: reverse
• rend:

  vector<int> myvector{ 1, 2, 3, 4, 5 };
   
  // using end() to print vector
  for (auto it = myvector.rbegin(); it != myvector.rend(); ++it)
      cout << ' ' << *it;
  

• cbegin: const, 不能修改vector里面的值
• cend:

  vector<int> myvector{ 1, 2, 3, 4, 5 };
   
  // using end() to print vector
  for (auto it = myvector.cbegin(); it != myvector.cend(); ++it)
      cout << ' ' << *it;
  

• crbegin: const, reverse
• crend:

Capacity

• size() – Returns the number of elements in the vector
• max_size() – Returns the maximum number of elements that the vector can hold.(这个应该是可以申请得到但是没申请的)
• capacity() – Returns the size of the storage space currently allocated to the vector expressed as number of elements.（这个是已经申请的）
• resize(n) – Resizes the container so that it contains ‘n’ elements.
• empty() – Returns whether the container is empty.
• shrink_to_fit() – Reduces the capacity of the container to fit its size and destroys all elements beyond the capacity.
• reserve() – Requests that the vector capacity be at least enough to contain n elements.

Element access:

• reference operator [g] – Returns a reference to the element at position ‘g’ in the vector
• at(g) – Returns a reference to the element at position ‘g’ in the vector
• front() – Returns a reference to the first element in the vector
• back() – Returns a reference to the last element in the vector
• data() – Returns a direct pointer to the memory array used internally by the vector to store its owned elements.

cout << "\nReference operator [g] : g1[2] = " << g1[2];

cout << "\nat : g1.at(4) = " << g1.at(4);

cout << "\nfront() : g1.front() = " << g1.front();

cout << "\nback() : g1.back() = " << g1.back();

// pointer to the first element
int* pos = g1.data();

cout << "\nThe first element is " << *pos;
return 0;

Modifiers:

• assign() – It assigns new value to the vector elements by replacing old ones

  vector<int> vect1{1, 2, 3, 4};
  
  // Declaring another vector
  vector<int> vect2;
  
  // Copying vector by assign function
  vect2.assign(vect1.begin(), vect1.end());
  

• push_back() – It push the elements into a vector from the back
• pop_back() – It is used to pop or remove elements from a vector from the back.
• insert() – It inserts new elements before the element at the specified position
• erase() – It is used to remove elements from a container from the specified position or range.
• swap() – It is used to swap the contents of one vector with another vector of same type. Sizes may differ.
• clear() – It is used to remove all the elements of the vector container
• emplace() – It extends the container by inserting new element at position
• emplace_back() – It is used to insert a new element into the vector container, the new element is added to the end of the vector(比push_back 快一点？不需要构造临时变量？)[²]

  std::vector<std::pair<std::string, std::string> > vec;
  vec.emplace_back(std::string("Hello"), std::string("world"));  
  

vector<int> v;

// fill the array with 10 five times
v.assign(5, 10);

cout << "The vector elements are: ";
for (int i = 0; i < v.size(); i++)
    cout << v[i] << " ";

// inserts 15 to the last position
v.push_back(15);
int n = v.size();
cout << "\nThe last element is: " << v[n - 1];

// removes last element
v.pop_back();

// prints the vector
cout << "\nThe vector elements are: ";
for (int i = 0; i < v.size(); i++)
    cout << v[i] << " ";

// inserts 5 at the beginning
v.insert(v.begin(), 5);

cout << "\nThe first element is: " << v[0];

// removes the first element
v.erase(v.begin());

cout << "\nThe first element is: " << v[0];

// inserts at the beginning
v.emplace(v.begin(), 5);
cout << "\nThe first element is: " << v[0];

// Inserts 20 at the end
v.emplace_back(20);
n = v.size();
cout << "\nThe last element is: " << v[n - 1];

// erases the vector
v.clear();
cout << "\nVector size after erase(): " << v.size();

unordered_set

• insert()– Insert a new {element} in the unordered_set container.
• begin()– Return an iterator pointing to the first element in the unordered_set container.
• end()– Returns an iterator pointing to the past-the-end-element. count()– Count occurrences of a particular element in an unordered_set container.
• find()– Search for an element in the container.
• clear()– Removes all of the elements from an unordered_set and empties it.
• cbegin()– Return a const_iterator pointing to the first element in the unordered_set container.
• cend()– Return a const_iterator pointing to past-the-end element in the unordered_set container or in one of it’s bucket.
• bucket_size()– Returns the total number of elements present in a specific bucket in an unordered_set container.
• erase()– Remove either a single element or a range of elements ranging from start(inclusive) to end(exclusive).
• size()– Return the number of elements in the unordered_set container.
• swap()– Exchange values of two unordered_set containers.
• emplace()– Insert an element in an unordered_set container.
• max_size()– Returns maximum number of elements that an unordered_set container can hold.
• empty()– Check if an unordered_set container is empty or not. equal_range– Returns range that includes all elements equal to given value.
• operator= – Copies (or moves) an unordered_set to another unordered_set and unordered_set::operator= is the corresponding operator function.
• hash_function() – This hash function is a unary function which takes asingle argument only and returns a unique value of type size_t based on it.
• reserve()– Used to request capacity change of unordered_set.
• bucket()– Returns the bucket number of a specific element.
• bucket_count() – Returns the total number of buckets present in an unordered_set container.
• load_factor()– Returns the current load factor in the unordered_set container.
• rehash()– Set the number of buckets in the container of unordered_set to given size or more.
• max_load_factor()– Returns(Or sets) the current maximum load factor of the unordered set container.
• emplace_hint()– Inserts a new element in the unordered_set only if the value to be inserted is unique, with a given hint.
• == operator – The ‘==’ is an operator in C++ STL performs equality comparison operation between two unordered sets and unordered_set::operator== is the corresponding operator function for the same.
• key_eq()– Returns a boolean value according to the comparison. It returns the key equivalence comparison predicate used by the unordered_set.
• operator!=– The != is a relational operator in C++ STL which compares the equality and inequality between unordered_set containers.
• max_bucket_count() – Find the maximum number of buckets that unordered_set can have.

参考文献