unordered_multimap::begin()
描述 (Description)
C ++函数std::unordered_multimap::begin()返回一个指向其中一个桶中第一个元素的迭代器。
声明 (Declaration)
以下是std :: unordered_multimap :: begin()函数形式std :: unordered_map()头的声明。
C++11
local_iterator begin(size_type n);
const_local_iterator begin(size_type n) const;
参数 (Parameters)
n - 桶号,必须小于bucket_count 。
返回值
如果object是常量限定的,则method返回常量迭代器,否则返回非常量引用。
时间复杂
常数即O(1)
例子 (Example)
以下示例显示了std :: unordered_multimap :: begin()函数的用法。
#include <iostream>
#include <unordered_map>
using namespace std;
int main(void) {
unordered_multimap<char, int> umm = {
{'a', 1},
{'b', 2},
{'c', 3},
{'d', 4},
{'e', 5}
};
cout << "Unordered multimap contains following elements" << endl;
for (int i = 0; i < umm.bucket_count(); ++i) {
cout << "Bucket " << i << " contains:" << endl;
for (auto it = umm.begin(i); it != umm.end(i); ++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 multimap contains following elements
Bucket 0 contains:
c = 3
Bucket 1 contains:
d = 4
Bucket 2 contains:
e = 5
Bucket 3 contains:
Bucket 4 contains:
Bucket 5 contains:
Bucket 6 contains:
Bucket 7 contains:
Bucket 8 contains:
Bucket 9 contains:
a = 1
Bucket 10 contains:
b = 2