C++多重映射 cend()函数用于返回常量迭代器,该常量迭代器位于多重映射中最后一个条目之后。
const_iterator cend() const noexcept; //since C++ 11
const_iterator 是指向常量内容的迭代器。
它返回一个常量迭代器,该迭代器指向multimap的最后一个元素。
让我们看一下cend()函数的简单示例:
#include <iostream> #include <map> using namespace std; int main () { multimap<char,string> mymultimap; mymultimap = { {'a',"Java"}, {'b', "C++"}, {'b', "Python"}, {'a', "Android"} }; //print content: cout << "mymultimap contains:"; for (auto it = mymultimap.cbegin(); it != mymultimap.cend(); ++it) cout << " [" << (*it).first << ':' << (*it).second << ']'; cout << '\n'; return 0; }
输出:
mymultimap contains: [a:Java] [a:Android] [b:C++] [b:Python]
在上面的示例中,cend()函数用于返回指向mymultimap多重映射中最后一个元素旁边的const_迭代器。
让我们看一个简单的示例,使用for-each循环遍历multimap:
#include <iostream> #include <map> #include <string> #include <iterator> #include <algorithm> using namespace std; int main() { multimap<string, int> m; m= { {"Room1", 100}, {"Room2", 200}, {"Room1", 300}, {"Room1", 100} }; // Create a multimap iterator and point to beginning of multimap multimap<string, int>::iterator it = m.begin(); // Iterate over a multimap using std::for_each and Lambda function for_each(m.cbegin(), m.cend(), [](pair<string, int> element){ // Accessing KEY from element string word = element.first; // Accessing VALUE from element. int count = element.second; cout<<word<<" = "<<count<<endl; }); return 0; }
输出:
Room1 = 100 Room1 = 300 Room1 = 100 Room2 = 200
在上面的示例中,我们使用STL算法std ::for-each迭代multimap。它将在每个multimap元素上进行迭代,并调用我们提供的回调。
让我们看一个简单的示例,使用while循环遍历multimap:
#include <iostream> #include <map> #include <string> int main() { using namespace std; multimap<int,string> mymultimap = { { 100, "Nikita"}, { 100, "Deep" }, { 200, "Priya" }, { 300, "Suman" }, { 200, "Aman" }}; multimap<int, string>::const_iterator it;//declare an iterator it = mymultimap.cbegin();//assign it to the start of the vector while (it != mymultimap.cend())//while it hasn't reach the end { cout << it->first << " = " << it->second << "\n"; // prin the value of the element it points to ++it;//and iterate to the next element } cout << endl; }
输出:
100 = Nikita 100 = Deep 200 = Priya 200 = Aman 300 = Suman
在上面的示例中,cend()函数用于返回指向mymultimap多重映射中最后一个元素旁边的const_iterator。
让我们看一个简单的例子:
#include <iostream> #include <string> #include <map> using namespace std; int main () { multimap<int,int> mymultimap = { { 10, 10}, { 20, 20 }, { 10, 30 } }; cout<<"Elements are:" <<endl; for (auto it = mymultimap.cbegin(); it != mymultimap.cend(); ++it) cout << it->first << " + " << it->second << " = " <<it->first + it->second << '\n'; auto ite = mymultimap.cend(); cout << "end element (point next to the last): "; cout << "{" << ite->first << ", " << ite->second << "}\n"; return 0; }
输出:
Elements are: 10 + 10 = 20 10 + 30 = 40 20 + 20 = 40 end element (point next to the last): {3, 0}
在上面的示例中,cend()函数用于返回指向mymultimap多重映射中最后一个元素旁边的const_iterator。
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