C++ set search for pair element?

Question

So I have a set of pairs<string ,string>

And I want to use find() to search for a single string which would be in the "first" of the pair, then if I find that string in first I want to return second from that function.

My current attempt is..

myList::iterator i;

i = theList.find(make_pair(realName, "*"));

return i->second;

Answer 1

Is C++11 acceptable?

auto it = find_if(theList.begin(), theList.end(),
    [&](const pair<string, string>& val) -> bool {
        return val.first == realName;
    });

return it->second;

Or in C++03, first define a functor:

struct MatchFirst
{
        MatchFirst(const string& realName) : realName(realName) {}

        bool operator()(const pair<string, string>& val) {
                return val.first == realName;
        }

        const string& realName;
};

then call it like so:

myList::iterator it = find_if(a.begin(), a.end(), MatchFirst(realName));
return it->second;

This will only return the first match, but from your question, it looks like that's all you're expecting.

Answer 2

You can use std::set<std::pair<std::string, std::string> > for this but you will need a custom comparison object for this because the pair's relational operator takes both elements for this. That said, it seems as if you actually should use a std::map<std::string, std::string> instead.