C++ unordered_map::bucket() 函数

C++ 函数unordered_map::bucket()函数返回键为k的元素所在的桶号。桶是容器哈希表中的一个内存空间，元素根据其键的哈希值分配到该空间。桶的有效范围是从 0 到bucket_count - 1.

语法

以下是 std::unordered_map::bucket() 函数的语法。

size_type bucket(const key_type& k) const;

参数

• k − 表示要查找其桶的键。

返回值

返回无符号整型，表示对应于键k.

示例 1

在下面的示例中，我们将演示 unordered_map::bucket() 函数的用法。

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void){
   unordered_map<char, int> um = {
      {'a', 1},
      {'b', 2},
      {'c', 3},
      {'d', 4},
      {'e', 5}
   };
   for (auto it = um.begin(); it != um.end(); ++it) {
      cout << "Element " << "[" << it->first  << " : "<< it->second << "] " << "is in "<< um.bucket(it->first) << " bucket." << endl; 
   }
   return 0;
}

输出

以下是上述代码的输出：

Element [e : 5] is in 3 bucket.
Element [d : 4] is in 2 bucket.
Element [c : 3] is in 1 bucket.
Element [b : 2] is in 0 bucket.
Element [a : 1] is in 6 bucket.

示例 2

在下面的示例中，我们创建一个只存储字符串值的 unordered_map，并计算当前 unordered_map 中分配给每个名称的桶数。

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void) {
   unordered_map<string, string> um = {
      {"Aman", "Ranchi"},
      {"Vivek", "Kanpur"},
      {"Akash", "Daltonganj"},
      {"Revathi", "Wrangle"},
      {"Sarika", "Banaras"}
   };
   for (auto it = um.begin(); it != um.end(); ++it) {
      cout << "Element " << "[" << it->first  << " : "
          << it->second << "] " << "is in " 
          << um.bucket(it->first) << " bucket." << endl;
   }
   return 0;
}

输出

以下是上述代码的输出：

Element [Sarika : Banaras] is in 9 bucket.
Element [Revathi : Wrangle] is in 10 bucket.
Element [Akash : Daltonganj] is in 5 bucket.
Element [Vivek : Kanpur] is in 4 bucket.
Element [Aman : Ranchi] is in 8 bucket.

示例 3

考虑下面的示例，我们将显示从 unordered_map 中指向容器第一个元素的迭代器的桶数。

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void) {
   unordered_map<string, string> um = {
      {"Aman", "Ranchi"},
      {"Vivek", "Kanpur"},
      {"Akash", "Daltonganj"},
      {"Revathi", "Wrangle"},
      {"Sarika", "Banaras"}
   };
    // prints the bucket number of the beginning element
    auto it = um.begin();
    // stores the bucket number of the key k
    int number = um.bucket(it->first);
    cout << "The bucket number of key " << it->first << " is " << number;
   return 0;
}

输出

让我们编译并运行上面的程序，这将产生以下结果：

The bucket number of key Sarika is 9