C++ set cbegin()函数用于返回指向set集合的第一个元素的常量迭代器。
const_iterator cbegin() const noexcept; //since C++ 11
const_iterator 是指向常量内容的迭代器。
它返回一个const_iterator指向集合的第一个元素。
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让我们看一下cbegin()函数的简单示例:
#include <iostream> #include <set> using namespace std; int main () { set<string> myset= {"Java", "C++","SQL"}; //show content: for (auto it = myset.cbegin(); it != myset.cend(); ++it) cout <<*it << '\n'; return 0; }
输出:
C++ Java SQL
在上面的示例中,cbegin()函数用于返回指向myset集合中第一个元素的常量迭代器。
让我们看一个简单的例子:
#include <set> #include <iostream> int main( ) { using namespace std; set <int> s1; set <int>::iterator s1_Iter; set <int>::const_iterator s1_cIter; 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 ); //The following 2 lines would err because the iterator is const //s1_cIter = s1.begin( ); //s1.erase( s1_cIter ); s1_cIter = s1.begin( ); cout << "The first element of s1 is now " << *s1_cIter << endl; }
输出:
The first element of s1 is 1 The first element of s1 is now 2
让我们看一个简单的示例,使用while循环遍历集合:
#include <iostream> #include <set> #include <string> int main() { using namespace std; set<string> myset = {"Robin","Dolly", "John","Nikita"}; set<string>::const_iterator it;//declare an iterator it = myset.cbegin();//assign it to the start of the vector while (it != myset.cend())//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:
Dolly John Nikita Robin
在上面的示例中,cbegin()函数用于返回指向myset集合中第一个元素的迭代器。
让我们看另一个简单的例子:
#include <iostream> #include <string> #include <set> using namespace std; int main () { set<int> number = {400, 350, 465, 290, 410}; cout << "Increasing order: " << '\n'; cout<<"______________________\n"; set<int>::const_iterator cit; for (cit=number.cbegin(); cit!=number.cend(); ++cit) cout << *cit<< '\n'; auto low = number.cbegin(); auto high = number.rbegin(); cout << "\nSmallest Number is: "<< *low <<endl; cout<< "Biggest Number is: "<<*high <<endl; return 0; }
输出:
Increasing order: ______________________ 290 350 400 410 465 Smallest Number is: 290 Biggest Number is: 465
在上面的示例中,cbegin()函数用于返回指向myset集合中第一个元素的迭代器。
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