C++ swap(multimap)是C++中multimap的非成员函数。这用于交换两个multimap(即x和y)的内容,但两个multimap都必须为相同类型,尽管大小可能不同。
template <class Key, class T, class Compare, class Alloc> void swap (multimap<Key,T,Compare,Alloc>& x, multimap<Key,T,Compare,Alloc>& y);
x :第一个multimap对象。
y :第二个相同类型的multimap对象。
没有
让我们看一下将一个multimap的元素交换到另一个的简单示例:
#include <iostream> #include <map> using namespace std; int main(void) { multimap<char, int> m1 = { {'a', 1}, {'b', 2}, {'c', 3}, {'b', 4}, {'e', 5}, }; multimap<char, int> m2; swap(m1, m2); cout << "Multimap contains following elements" << endl; for (auto it = m2.begin(); it != m2.end(); ++it) cout << it->first << " = " << it->second << endl; return 0; }
输出:
Multimap contains following elements a = 1 b = 2 b = 3 c = 4 e = 5
在上面的示例中,multimapm1具有五个元素,而m2为空。当您将m1交换为m2时,m1的所有元素都将交换为m2。
让我们看一个简单的示例来交换两个multimap的内容:
#include <iostream> #include <map> using namespace std; int main () { multimap<char,int> multimap1,multimap2; multimap1 = { {'x', 100}, {'y', 200} }; multimap2= { {'a', 110}, {'c', 220}, {'c', 330} }; swap(multimap1,multimap2); cout << "multimap1 contains:\n"; for (multimap<char,int>::iterator it=multimap1.begin(); it!=multimap1.end(); ++it) cout << it->first << " => " << it->second << '\n'; cout << "multimap2 contains:\n"; for (multimap<char,int>::iterator it=multimap2.begin(); it!=multimap2.end(); ++it) cout << it->first << " => " << it->second << '\n'; return 0; }
输出:
multimap1 contains: a => 110 c => 220 c => 330 multimap2 contains: x => 100 y => 200
在上面的例子中,两个multimap的内容,即multimap1和multimap2相互交换。
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让我们看一个简单的示例,以交换两个multimap的内容:
#include <iostream> #include <map> using namespace std; template <class Multimap> void print(const char* name, const Multimap& m) { cout << name << " : {"; for (const auto& x : m) { cout << "[" << x.first << "," << x.second << "], "; } cout << "}" << endl; } int main() { multimap<int, char> m1; m1.insert(std::make_pair(10, 'a')); m1.insert(std::make_pair(20, 'b')); m1.insert(std::make_pair(10, 'c')); multimap<int, char> m2; m2.insert(std::make_pair(5, 'd')); m2.insert(std::make_pair(15, 'e')); //Swap m1 and m2 swap(m1, m2); print("m1", m1); print("m2", m2); }
输出:
m1 : {[5,d], [15,e], } m2 : {[10,a], [10,c], [20,b], }
让我们看一个简单的例子:
#include <iostream> #include <string> #include <map> using namespace std; void show(const char *msg, multimap<string, int> mp); int main() { multimap<string, int> m1, m2; m1.insert(pair<string, int>("A", 100)); m1.insert(pair<string, int>("G", 300)); m1.insert(pair<string, int>("B", 200)); //Exchange the contents of m1 and m2. cout << "Exchange m1 and m2.\n"; swap(m1,m2); show("Contents of m2: ", m2); show("Contents of m1: ", m1); //Clear m1. m1.clear(); if(m1.empty()) cout << "m1 is now empty."; return 0; } // Display the contents of a multimap<string, int> by using an iterator. void show(const char *msg, multimap<string, int> mp) { multimap<string, int>::iterator itr; cout << msg << endl; for(itr=mp.begin(); itr != mp.end(); ++itr) cout << " " << itr->first << ", " << itr->second << endl; cout << endl; }
输出:
Exchange m1 and m2. Contents of m2: A, 100 B, 200 G, 300 Contents of m1: m1 is now empty.
在上面的示例中,将multimap m1的内容交换到multimap m2,并且在清除了交换m1后,multimap已被清除。
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