cbegin
描述 (Description)
它返回一个指向unordered_set容器中第一个元素的const_iterator。
声明 (Declaration)
以下是std :: unordered_set :: cbegin的声明。
C++11
const_iterator cbegin() const noexcept;
参数 (Parameters)
n - 它包含有关桶号的信息。
返回值
它返回一个指向unordered_set容器中第一个元素的const_iterator。
异常 (Exceptions)
如果任何元素比较对象抛出异常,则抛出异常。
请注意,无效参数会导致未定义的行为。
时间复杂
恒定时间。
例子 (Example)
以下示例显示了std :: unordered_set :: cbegin的用法。
#include <iostream>
#include <string>
#include <unordered_set>
int main () {
std::unordered_set<std::string> myset =
{"100","200","300","400","500","600","700","800"};
std::cout << "myset contains:";
for ( auto it = myset.cbegin(); it != myset.cend(); ++it )
std::cout << " " << *it; // cannot modify *it
std::cout << std::endl;
std::cout << "myset's buckets contain:\n";
for ( unsigned i = 0; i < myset.bucket_count(); ++i) {
std::cout << "bucket #" << i << " contains:";
for ( auto local_it = myset.cbegin(i); local_it!= myset.cend(i); ++local_it )
std::cout << " " << *local_it;
std::cout << std::endl;
}
return 0;
}
让我们编译并运行上面的程序,这将产生以下结果 -
myset contains: 700 600 400 800 200 500 300 100
myset's buckets contain:
bucket #0 contains:
bucket #1 contains:
bucket #2 contains:
bucket #3 contains:
bucket #4 contains: 700
bucket #5 contains:
bucket #6 contains: 400
bucket #7 contains: 500 300 100
bucket #8 contains: 600
bucket #9 contains: 800 200
bucket #10 contains: