C++ 学习小程序之　map 的用法-白红宇

C++ 学习小程序之　map 的用法

阅读量：7098 次

发布时间：2019-06-28

本文共 2637 字，大约阅读时间需要 8 分钟。

１．　map::at

1 #include 
     
       2 #include 
      
        3 #include 
        4 using namespace std; 5  6 int main(){ 7     map
        
          mymap = { 8         {
   "alpha", 0}, 9         {
   "beta", 0},10         {
   "gamma", 0}};11 12     mymap.at("alpha") = 10;13     mymap.at("beta") = 20;14     mymap.at("gamma") = 30;15 16     for (auto& x:mymap){17         cout<
         
          <<": "<
          
           <<'\n';18 }19 20 return 0;21 }

２．　make_pair example

1 // make_pair example 2 #include 
     
            // std::pair 3 #include 
      
            // std::cout 4  5 int main () { 6   std::pair 
       
         foo; 7   std::pair 
        
          bar; 8  9   foo = std::make_pair (10,20);10   bar = std::make_pair (10.5,'A'); // ok: implicit conversion from pair
         
          11 12   std::cout << "foo: " << foo.first << ", " << foo.second << '\n';13   std::cout << "bar: " << bar.first << ", " << bar.second << '\n';14 15   return 0;16 }

３．　map::begin/end

1 // map::begin/end 2 #include 
     
       3 #include 
       4  5 int main () 6 { 7   std::map
       
         mymap; 8  9   mymap['b'] = 100;10   mymap['a'] = 200;11   mymap['c'] = 300;12 13   // show content:14   for (std::map
        
         ::iterator it=mymap.begin(); it!=mymap.end(); ++it)15     std::cout << it->first << " => " << it->second << '\n';16 17   return 0;18 }

4. map::insert(C++98)

1 // map::insert(C++98) 2 #include 
     
       3 #include 
       4 using namespace std; 5 int main () 6 { 7     map
       
         mymap; 8  9     // first insert function version (single parameter):10     mymap.insert ( pair
        
         ('a', 100) );11     mymap.insert ( pair
         
          ('z', 200) );12 13     pair
          
           
            ::iterator, bool> ret;14 ret = mymap.insert (pair
            
             ('z',500));15 if (ret.second == false){16 cout<<"element 'z' already existed";17 cout<<"with a value of " << ret.first->second << '\n';18 }19 20 //second insert function version (with hint position):21 map
             
              ::iterator it = mymap.begin();22 mymap.insert (it, pair
              
               ('b',300)); // max efficiency inserting23 mymap.insert (it, pair
               
                ('c',400)); // no max efficiency inserting24 25 //third insert function version (range insertion):26 map
                
                  anothermap;27 anothermap.insert(mymap.begin(),mymap.find('c'));28 29 // showing contents:30 cout<<"mymap contains: \n";31 for (it = mymap.begin(); it!= mymap.end(); ++it)32 cout<
                 
                  first<<"=>"<
                  
                   second<<'\n';33 34 cout<<"anothermap contains: \n";35 for(it=anothermap.begin(); it!=anothermap.end();++it)36 cout<
                   
                    first<<"=>"<
                    
                     second<<'\n';37 38 return 0;39 }