C++ Unordered_map erase()用法及代码示例

描述

C++ 函数std::unordered_map::erase()删除与键关联的映射值k。

声明

以下是 std::unordered_map::erase() 函数形式 std::unordered_map 头文件的声明。

C++11

size_type erase(const key_type& k);

参数

k─ 要删除的元素的键。

返回值

返回移除的元素数。

时间复杂度

常数，即 O(1)

示例

下面的例子展示了 std::unordered_map::erase() 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}
            };

   cout << "Unordered map contains following elements before erase operation" << endl;

   for (auto it = um.begin(); it != um.end(); ++it)
      cout << it->first << " = " << it->second << endl;

   um.erase('a');

   cout << endl;
   cout << "Unordered map contains following elements after erase operation" << endl;

   for (auto it = um.begin(); it != um.end(); ++it)
      cout << it->first << " = " << it->second << endl;

   return 0;
}

让我们编译并运行上面的程序，这将产生以下结果——

Unordered map contains following elements before erase operation
e = 5
a = 1
b = 2
c = 3
d = 4
Unordered map contains following elements after erase operation
e = 5
b = 2
c = 3
d = 4