STL之deque雙向隊列

deque雙向隊列是一種雙向開口的連續線性空間，能夠高效的在頭尾兩端插入和刪除元素，提供隨機訪問，deque在接口上和vector很是類似，下面列出deque的經常使用成員函數：

Table 6.9. Constructors and Destructor of Deques

Operation	Effect
deque<Elem> c	Creates an empty deque without any elements
deque<Elem> c1(c2)	Creates a copy of another deque of the same type (all elements are copied)
deque<Elem> c(n)	Creates a deque with n elements that are created by the default constructor
deque<Elem> c(n,elem)	Creates a deque initialized with n copies of element elem
deque<Elem> c(beg,end)	Creates a deque initialized with the elements of the range [beg,end)
c.~deque<Elem>()	Destroys all elements and frees the memory

 

Table 6.10. Nonmodifying Operations of Deques

Operation	Effect
c.size()	Returns the actual number of elements
c.empty ()	Returns whether the container is empty (equivalent to size()==0, but might be faster)
c.max_size()	Returns the maximum number of elements possible
c1 == c2	Returns whether c1 is equal to c2
c1 != c2	Returns whether c1 is not equal to c2 (equivalent to ! (c1==c2))
c1 < c2	Returns whether c1 is less than c2
c1 > c2	Returns whether c1 is greater than c2 (equivalent to c2<c1)
c1 <= c2	Returns whether c1 is less than or equal to c2 (equivalent to ! (c2<c1) )
c1 >= c2	Returns whether c1 is greater than or equal to c2 (equivalent to ! (c1<c2) )
c.at(idx)	Returns the element with index idx (throws range error exception if idx is out of range)
c[idx]	Returns the element with index idx (no range checking)
c.front()	Returns the first element (no check whether a first element exists)
c.back()	Returns the last element (no check whether a last element exists)
c.begin()	Returns a random access iterator for the first element
c.end()	Returns a random access iterator for the position after the last element
c.rbegin()	Returns a reverse iterator for the first element of a reverse iteration
c.rend()	Returns a reverse iterator for the position after the last element of a reverse iteration

Table 6.11. Modifying Operations of Deques

Operation	Effect
c1 = c2	Assigns all elements of c2 to c1
c.assign (n,elem)	Assigns n copies of element elem
c.assign (beg,end)	Assigns the elements of the range [beg,end)
c1.swap(c2)	Swaps the data of c1 and c2
swap(c1,c2)	Same (as global function)
c.insert (pos,elem)	Inserts at iterator position pos a copy of elem and returns the position of the new element
c. insert (pos,n,elem)	Inserts at iterator position pos n copies of elem (returns nothing)
c.insert (pos,beg,end)	Inserts at iterator position pos a copy of all elements of the range [beg,end) (returns nothing)
c.push_back (elem)	Appends a copy of elem at the end
c.pop_back()	Removes the last element (does not return it)
c.push_front (elem)	Inserts a copy of elem at the beginning
c.pop_front()	Removes the first element (does not return it)
c.erase(pos)	Removes the element at iterator position pos and returns the position of the next element
c.erase (beg,end)	Removes all elements of the range [beg,end) and returns the position of the next element
c. resize (num)	Changes the number of elements to num (if size () grows, new elements are created by their default constructor)
c.resize (num, elem)	Changes the number of elements to num (if size () grows, new elements are copies of elem)
c.clear()	Removes all elements (makes the container empty)

 

　　deque的實現比較複雜，內部會維護一個map（注意！不是STL中的map容器）即一小塊連續的空間，該空間中每一個元素都是指針，指向另外一段（較大的）區域，這個區域稱爲緩衝區，緩衝區用來保存deque中的數據。所以deque在隨機訪問和遍歷數據會比vector慢。具體的deque實現能夠參考《STL源碼剖析》，固然此書中使用的SGI STL與VS2008所使用的PJ STL的實現方法仍是有區別的。下面給出了deque的結構圖：

因爲篇幅問題，deque的實現細節就再也不深刻了，下面給出deque的使用範例：

// cont/deque1. cpp

   #include <iostream>
   #include <deque>
   #include <string>
   #include <algorithm>
   using namespace std;

   int main()
   {

       //create empty deque of strings
       deque<string> coll;

       //insert several elements
       coll.assign (3, string("string"));
       coll.push_back ("last string");
       coll.push_front ("first string");

       //print elements separated by newlines
       copy (coll.begin(), coll.end(),
             ostream_iterator<string>(cout,"\n"));
       cout << endl;

       //remove first and last element
       coll.pop_front();
       coll.pop_back();

       //insert ''another'' into every element but the first
       for (int i=1; i<coll.size(); ++i) {
           coll[i] = "another " + coll [i];

       }

       //change size to four elements
       coll.resize (4, "resized string");

       //print elements separated by newlines
       copy (coll.begin(), coll.end(),
             ostream_iterator<string>(cout,"\n"));

   }

The program has the following output:

					
   first string
   string
   string
   string
   last string

   string
   another string
   another string
   resized string