C++中的unordered_multimap运算符=

unordered_multimap :: 运算符=是C++ STL中的内置函数，它执行三种类型的任务，下面将对其进行说明。

1. 语法(从不同容器复制元素)：

   unordered_multimap_name1 operator= (unordered_multimap_name2)

   参数：该函数不接受任何参数。右边的容器是将元素复制到左边的容器的容器。

   返回值：不返回任何内容。

   下面的程序说明了上述函数：

   // C++ program to illustrate the
   // unordered_multimap::operator=
   #include 
   using namespace std;
     
   int main()
   {
     
       // declaration
       unordered_multimap sample1, sample2;
     
       // inserts key and element
       // in sample1
       sample1.insert({ 10, 100 });
       sample1.insert({ 50, 500 });
     
       cout << "Key and Elements of Sample1 before copy  are:";
       for (auto it = sample1.begin(); it != sample1.end(); it++) {
           cout << "{" << it->first << ", " << it->second << "} ";
       }
     
       cout << "\nThe size of sample2 before copy: "
            << sample2.size();
     
       // opeator= to copy
       sample2 = sample1;
     
       cout << "\nKey and Elements of Sample2 after copy are: ";
       for (auto it = sample2.begin(); it != sample2.end(); it++) {
           cout << "{" << it->first << ", " << it->second << "} ";
       }
     
       return 0;
   }
   

   输出：

   Key and Elements of Sample1 before copy  are:{50, 500} {10, 100} 
   The size of sample2 before copy: 0
   Key and Elements of Sample2 after copy are: {50, 500} {10, 100}
   

2. 语法(用于从不同容器中移动元素)：

   unordered_multimap_name1 operator= (unordered_multimap_name2)

   参数：该函数不接受任何参数。右侧的容器是将元素从中移至左侧的容器的容器。使用运算符=后，右侧容器中的元素将被销毁。

   返回值：不返回任何内容。

   下面的程序说明了上述函数：

   // C++ program to illustrate the
   // unordered_multimap::operator=
   #include 
   using namespace std;
     
   // Function to merge two lists
   unordered_multimap merge(unordered_multimap a,
                                        unordered_multimap b)
   {
       unordered_multimap temp(a);
       temp.insert(b.begin(), b.end());
       return temp;
   }
   int main()
   {
     
       // declaration
       unordered_multimap sample1, sample2, sample3;
     
       // inserts key and element
       // in sample1
       sample1.insert({ 'a', 'A' });
       sample1.insert({ 'g', 'G' });
     
       // inserts key and element
       // in sample1
       sample2.insert({ 'b', 'B' });
       sample2.insert({ 'c', 'C' });
       sample2.insert({ 'd', 'D' });
     
       cout << "Key and Elements of Sample1 are: ";
       for (auto it = sample1.begin(); it != sample1.end(); it++) {
           cout << "{" << it->first << ", " << it->second << "} ";
       }
     
       cout << "\nKey and Elements of Sample2 are: ";
       for (auto it = sample2.begin(); it != sample2.end(); it++) {
           cout << "{" << it->first << ", " << it->second << "} ";
       }
     
       // merging and moved
       sample3 = merge(sample1, sample2);
       sample1 = sample3;
     
       cout << "\n\nKey and Elements of Sample1 are: ";
       for (auto it = sample1.begin(); it != sample1.end(); it++) {
           cout << "{" << it->first << ", " << it->second << "} ";
       }
     
       return 0;
   }
   

   输出：

   Key and Elements of Sample1 are: {g, G} {a, A} 
   Key and Elements of Sample2 are: {d, D} {b, B} {c, C} 
   
   Key and Elements of Sample1 are: {c, C} {b, B} {d, D} {a, A} {g, G}
   

3. 语法(用于分配来自不同列表的元素)：

   unordered_multimap_name1 operator= (intitializer_list il)

   参数：它不接受任何参数，它在右边具有将分配给容器的列表。

   返回值：不返回任何内容。

   下面的程序说明了上述函数：

   // C++ program to illustrate the
   // unordered_multimap::operator=
   #include 
   using namespace std;
     
   int main()
   {
     
       // declaration by using operator=
       unordered_multimap sample1 = { { 1, 2 }, { 3, 4 }, { 5, 6 } };
     
       cout << "Key and Elements of Sample1 are: ";
       for (auto it = sample1.begin(); it != sample1.end(); it++) {
           cout << "{" << it->first << ", " << it->second << "} ";
       }
     
       // declaration by using operator=
       unordered_multimap sample2 = { { 'a', 'A' }, { 'b', 'B' }, { 'c', 'C' } };
     
       cout << "\n\nKey and Elements of Sample1 are: ";
       for (auto it = sample2.begin(); it != sample2.end(); it++) {
           cout << "{" << it->first << ", " << it->second << "} ";
       }
     
       return 0;
   }
   

   输出：

   Key and Elements of Sample1 are: {5, 6} {3, 4} {1, 2} 
   
   Key and Elements of Sample1 are: {c, C} {b, B} {a, A}
   

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