如何更新这种地图结构？

Question

我有一个std::map<boost::shared_ptr<some_class>, class_description> class_map;其中class_description是：

//Each service provides us with rules 
struct class_description 
{ 
    //A service must have 
    std::string name; 
      // lots of other stuff... 
}; 

，我有另一std::map<boost::shared_ptr<some_class>, class_description> class_map_new;

我需要从class_map_new插入对<boost::shared_ptr<some_class>, class_description>到class_map万一有在class_map之前，这样的name没有class_description。如何做这样的事情？

Answer 1

std::map::insert不允许重复，所以你可以简单地试图插入新的价值观：

//Each service provides us with rules 
struct class_description 
{ 
    //A service must have 
    std::string name; 
    // lots of other stuff... 
}; 

std::map<boost::shared_ptr<some_class>, class_description> class_map; 
std::map<boost::shared_ptr<some_class>, class_description> class_map_new; 

// insert the new values into the class_map 
// using C++0x for simplicity... 
for(auto new_obj = class_map_new.cbegin(), end = class_map_new.cend(); 
    new_obj != end; ++new_obj) 
{ 
    auto ins_result = class_map.insert(*new_obj); 

    if(false == ins_result.second) 
    { 
     // object was already present, 
     // ins_result.first holds the iterator 
     // to the current object 
    } 
    else 
    { 
     // object was successfully inserted 
    } 
} 

Answer 2

你需要的是一个“STL像”算法copy_if。没有一个，但你可以在网上找到一个例子，或者通过查看count_if和remove_copy_if的代码来编写自己的例子。