I have the following...
struct MessageLetter{
char letter;
int count;
MessageLetter(char letter, int freq)
: letter(letter), count(freq)
{}
};
...
std::map<char, MessageLetter> lList;
...
MessageLetter m = MessageLetter(letter,1);
lList[letter] = m;
When I try to compile I get...
no matching constructor for initialization of 'MessageLetter'
::new ((void*)__p) _Tp();
Gotta be something easy anyone have an idea?
lList[letter] = m;
This line actually defaultly constructs a MessageLetter then returns it by reference, you then assign m to it, calling operator=.
This means that MessageLetter requires a defualt constructor, like so:
MessageLetter() {}
or with C++11:
MessageLetter()=default;
if you don't intend to actually do anything in it.
You can also get away without having to defaultly construct using std::map::insert
lList.insert(std::make_pair(letter), m));
or emplace with c++11:
lList.emplace(letter, { letter, 1 });
http://en.cppreference.com/w/cpp/container/map/insert
list.emplace(std::piecewise_construct, std::forward_as_tuple(letter), std::forward_as_tuple(letter, 1));The operator[] for an std::map requires that the mapped type be default-constructible (since it first default constructs a new element, then returns a reference to it, and you then assign to that). This isn't the case for you. You should use insert or emplace instead:
lList.insert(std::make_pair(letter, MessageLetter(letter, 1)));
// or
lList.emplace(letter, MessageLetter(letter, 1));
Both functions return information about whether the insertion was possible (the key may already have existed) and location of the element with the given key.
