C++ STL中的双端队列

deque :: shrink_to_fit()是C++ STL中的内置函数，可减少容器的容量以适应其大小，并破坏超出该容量的所有元素。此函数不会减小容器的尺寸。当为容器分配的内存超过了所需的内存量时，将使用此函数，然后此函数释放已分配的额外内存量。

句法：

deque_name.shrink_to_fit()

参数：该函数不接受任何参数。
返回值：该函数不返回任何内容。

下面的程序说明了上述函数：
示例1

// C++ program to illustrate
// the deque::shrink_to_fit()
#include 
using namespace std;
  
int main()
{
  
    // Initialized deque
    deque d(10);
  
    for (int i = 0; i < 5; i++)
        d[i] = i;
  
    // Initial deque
    cout << " Deque size initially: " << d.size();
  
    cout << "\n Deque  elements are: ";
    for (int i = 0; i < 10; i++)
        cout << d[i] << " ";
  
    // changes the size of the Deque
    // but does not destroys the elements
    d.resize(7);
  
    cout << "\n Deque size after resize(7): "
         << d.size();
  
    cout << "\n Deque elements after resize(7) are: ";
    for (int i = 0; i < 10; i++)
        cout << d[i] << " ";
  
    // Shrinks to the size
    // till which elements are
    // destroys the elements after 5
    d.shrink_to_fit();
  
    cout << "\n Deque size after shrink_to_fit(): "
         << d.size();
  
    cout << "\n Deque elements after shrink_to_fit() are: ";
    for (int i = 0; i < 10; i++)
        cout << d[i] << " ";
  
    return 0;
}

输出：

Deque size initially: 10
Deque  elements are: 0 1 2 3 4 0 0 0 0 0 
Deque size after resize(7): 7
Deque elements after resize(7) are: 0 1 2 3 4 0 0 0 0 0 
Deque size after shrink_to_fit(): 7
Deque elements after shrink_to_fit() are: 0 1 2 3 4 0 0 0 0 0

示例2

// C++ program to illustrate
// the deque::shrink_to_fit()
#include 
using namespace std;
  
int main()
{
    // creating a deque
    deque d(100);
  
    cout << "Size of d is : " << d.size() << endl;
  
    // resizing
    d.resize(20);
  
    cout << "Size of d after resize is : " << d.size() << endl;
  
    d.shrink_to_fit();
    return 0;
}

输出：

Size of d is : 100
Size of d after resize is : 20

注意：对于容器大小不断变化的矢量，shrink_to_fit()函数非常有用。

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