public member function
<unordered_map>

std::unordered_map::empty

bool empty() const noexcept;
測試容器是否為空
返回一個boolvalue indicating whether the unordered_map container is empty, i.e. whether its size is0.

This function does not modify the content of the container in any way. To clear the content of an array object, member function unordered_map::clear exists.

引數



返回值

true如果容器大小為0, false否則為 false。

示例

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// unordered_map::empty
#include <iostream>
#include <unordered_map>

int main ()
{
  std::unordered_map<int,int> first;
  std::unordered_map<int,int> second = {{1,10},{2,20},{3,30}};
  std::cout << "first " << (first.empty() ? "is empty" : "is not empty" ) << std::endl;
  std::cout << "second " << (second.empty() ? "is empty" : "is not empty" ) << std::endl;
  return 0;
}

輸出
first is empty
second is not empty


複雜度

常量。

迭代器有效性

沒有變化。

另見