C++ Set begin()
C++ Set begin()
C++ Set begin()函数用于返回引用set容器第一个元素的迭代器。
语法
iterator begin(); //until C++ 11
const_iterator begin() const; //until C++ 11
iterator begin() noexcept; //since C++ 11
const_iterator begin() const noexcept; //since C++ 11
参数
无
返回值
它返回指向迭代器第一个元素的迭代器 Set 。
复杂度
常量。
迭代器有效性
没有变化。
数据争用
已访问容器。
异常安全
此函数从不抛出异常。
示例1
让我们看一下begin()函数的简单示例:
#include <iostream>
#include <set>
using namespace std;
int main ()
{
set<string> myset= {"Java", "C++", "SQL"};
// show content:
cout<<"Contents of myset are: "<<endl;
for (set<string>::iterator it=myset.begin(); it!=myset.end(); ++it)
cout << *it<< '\n';
return 0;
}
输出:
Contents of myset are:
C++
Java
SQL
在上面的示例中，begin()函数用于返回指向myset集合中第一个元素的迭代器。
示例2
让我们看一个简单的例子:
#include <iostream>
#include <set>
using namespace std;
int main()
{
set<int> c;
c.insert(5);
c.insert(2);
c.insert(4);
c.insert(1);
c.insert(0);
c.insert(9);
set<int>::iterator i = c.begin();
while (i != c.end())
cout << *i++ << " ";
cout << endl;
}
输出:
示例3
让我们看一个使用while循环对集合进行迭代的简单示例:
#include <iostream>
#include <set>
#include <string>
int main()
{
using namespace std;
set<string> myset = { "Nikita","Deep","Priya","Suman","Aman" };
cout<<"Elements of myset are: "<<endl;
set<string>::const_iterator it; // declare an iterator
it = myset.begin(); // assign it to the start of the set
while (it != myset.end()) // while it hasn't reach the end
{
cout << *it << "\n";
// print the value of the element it points to
++it; // and iterate to the next element
}
cout << endl;
}
输出:
Elements of myset are:
Aman
Deep
Nikita
Priya
Suman
在上面，begin()函数用于返回指向myset集中第一个元素的迭代器。
示例4
看一个简单的例子:
#include <set>
#include <iostream>
int main( )
{
using namespace std;
set <int> s1;
set <int>::iterator s1_Iter;
s1.insert( 1 );
s1.insert( 2 );
s1.insert( 3 );
s1_Iter = s1.begin( );
cout << "The first element of s1 is " << *s1_Iter << endl;
s1_Iter = s1.begin( );
s1.erase( s1_Iter );
s1_Iter = s1.begin( );
cout << "The first element of s1 is now " << *s1_Iter << endl;
}
输出:
The first element of s1 is 1
The first element of s1 is now 2
在上面的示例中，begin()函数用于返回指向myset集中第一个元素的迭代器。
