Re: [Boost-users] [lambda] Defining a predicate for std::find_if if the key to a std::map is std::pair

Ryan McConnehey wrote:

...

std::pair inserted = myMap.insert(cMap::value_type(cMap::key_type(givenName, properInt), cmap::mapped_type())); if (! inserted.second) // oh, it already existed? { ... }

Since I'm using both givenName and properInt as a key, the insert will never return false for just a duplicate of givenName.

Forgive me if this is a stupid question, but if you don't want to compare the int, why is it part of the key at all?

Also, if the insert did return false then it means a good value at that map key has been replaced. The reason I'm trying to catch this duplication is because "last value entered wins" doesn't meet the requirement I was given.

Not true. When insert() finds an existing key, it returns a std::pair with the iterator to that entry and 'false' meaning it wasn't newly inserted. Per Stroustrup: "The operation m.insert(val) attempts to add a (Key, T) pair val to m. Since maps rely on unique keys, insertion takes place only if there is not already an element in the m with that key. The return value of m.insert(val) is a pair. The bool is true if val was actually inserted. The iterator refers to the element of m holding the key k." ... "In fact, [] is little more than a convenient notation for insert(). The result of m[k] is equivalent to the result of (*(m.insert(make_pair(k,V())).first)).second, where V() is the default value for the mapped type."