stdmap

Since there is no .resize() member function in C++ std::map I was wondering, how one can get a std::map with at most n elements. The obvious solution is to create a loop from 0 to n and use the nth iterator as the first parameter for std::erase(). I was wondering if there is any solution that does not need the loop (at least not in my user code) and is more "the STL way to go". You can use std::advance( iter, numberofsteps ) for that. Universal solution for almost any container, such as std::list, std::map, boost::multi_index. You must check the size of your map only. template<class It> It

In my C++ application, I have some values that act as codes to represent other values. To translate the codes, I've been debating between using a switch statement or an stl map. The switch would look something like this: int code; int value; switch(code) { case 1: value = 10; break; case 2: value = 15; break; } The map would be an stl::map<int, int> and translation would be a simple lookup with the code used as the key value. Which one is better/more efficient/cleaner/accepted? Why? Personally, I would use the map, as its use implies a data lookup - using a switch usually indicates a

Which way to assign values to a map is most efficient? Or are they all optimized to the same code (on most modern compilers)? // 1) Assignment using array index notation Foo["Bar"] = 12345; // 2) Assignment using member function insert() and STL pair Foo.insert(std::pair<string,int>("Bar", 12345)); // 3) Assignment using member function insert() and "value_type()" Foo.insert(map<string,int>::value_type("Bar", 12345)); // 4) Assignment using member function insert() and "make_pair()" Foo.insert(std::make_pair("Bar", 12345)); (I know I could benchmark and check compiler output, but this question

According to this you cannot reserve space for std::map : No, the members of the map are internally stored in a tree structure. There is no way to build the tree until you know the keys and values that are to be stored. From this it is obvious why std::map would lack a reserve() method, which it does on cppreference.com. However, std::unordered_map does have a reserve() method, but when I try to use it with operator[] , insert() or emplace() they all go to allocate memory despite me having called reserve() first. What's up with this? Why won't reserve() properly reserve the required space? And

I have the following code, but I get an error on on the last line: struct coord { int x, y; bool operator=(const coord &o) { return x == o.x && y == o.y; } bool operator<(const coord &o) { return x < o.x || (x == o.x && y < o.y); } }; map<coord, int> m; pair<coord, int> p((coord{0,0}),123); m.insert(p); // ERROR here How can I use a struct as key in a map? I tried to change the code to this: struct coord { int x, y; bool const operator==(const coord &o) { return x == o.x && y == o.y; } bool const operator<(const coord &o) { return x < o.x || (x == o.x && y < o.y); } }; But I'm still getting

I have a small problem during debugging my App in VS 2010 RC when I want to see all the elements of std::map container. When debugger reaches the breakpoint and I want to check the values of the map in element inspector (in 'Locals' windows and in pop-up windows after hovering the variable name with mouse as well) and I'm scrolling down the list of the elements it stops on the 100 element and I can't next elements. The map contains more than 200 elements (map's counter parameter shows this properly) but I can't view them all in the element inspector. The problem appears even in the most simple