insert is not a recommended way – it is one of the ways to insert into map. The difference with operator[] is that the insert can tell whether the element is inserted into the map. Also, if your class has no default constructor, you are forced to use insert. operator[] needs the default constructor because … Read more
No, there isn’t. The simplest solution is to write your own free template function to do this. Something like: #include <string> #include <map> using namespace std; template <typename K, typename V> V GetWithDef(const std::map <K,V> & m, const K & key, const V & defval ) { typename std::map<K,V>::const_iterator it = m.find( key ); if … Read more
As of C++11, you have two major additional options. First, you can use insert() with list initialization syntax: function.insert({0, 42}); This is functionally equivalent to function.insert(std::map<int, int>::value_type(0, 42)); but much more concise and readable. As other answers have noted, this has several advantages over the other forms: The operator[] approach requires the mapped type to … Read more
When you write map[key] = value; there’s no way to tell if you replaced the value for key, or if you created a new key with value. map::insert() will only create: using std::cout; using std::endl; typedef std::map<int, std::string> MyMap; MyMap map; // … std::pair<MyMap::iterator, bool> res = map.insert(MyMap::value_type(key,value)); if ( ! res.second ) { cout … Read more
While your solution should work, it can be difficult to read depending on the skill level of your fellow programmers. Additionally, it moves functionality away from the call site. Which can make maintenance a little more difficult. I’m not sure if your goal is to get the keys into a vector or print them to … Read more
Using C++11: #include <map> using namespace std; map<int, char> m = {{1, ‘a’}, {3, ‘b’}, {5, ‘c’}, {7, ‘d’}}; Using Boost.Assign: #include <map> #include “boost/assign.hpp” using namespace std; using namespace boost::assign; map<int, char> m = map_list_of (1, ‘a’) (3, ‘b’) (5, ‘c’) (7, ‘d’);