我如何进入一对双 <pair<string,string> ，double&gt;在C ++ 11中

Question

I am looking to increment the double of a pair when iterating through a map.

The map is created as such:

typedef pair<string,string> Name;
map<Name,double> paidEmploy;

After I get everything from cin and add it to the map, it will not add an object if the name is already in the map (obviously). If the insert then fails, I loop through the map to find the position of the already inserted name. I then want to access the double of the map to increment by the next amount. How do I access this?

Here is what I'm doing so far:

map<Name,double> paidEmploy;
string line, fn, ln, date;
double paid;
while(getline(cin, line)){
    istringstream(line) >> date >> fn >> ln >> paid; // assume all lines are correct
    if(paidEmploy.insert(pair<pair<string,string>,double>(pair<string,string>(fn,ln),paid)).second == false){
        for(auto it = paidEmploy.begin(); it != paidEmploy.end(); it++){
            if(it->second.first == fn && it->second.second == ln){
                it->third += paid;
                break;
            }
        }
    }
}

Answer 1

In your case, you may simply do:

paidEmploy[std::make_pair(fn, ln)] += paid;

Or if really you want to use insert result:

auto p = paidEmploy.insert(pair<pair<string, string>, double>(std::make_pair(fn, ln), paid));

if (p.second == false) {
    p.first.second += paid;
}

Answer 2

 for(auto it = paidEmploy.begin(); it != paidEmploy.end(); it++){
            if(it->fist.first == fn && it->fist.second == ln){
                it->second += paid;
                break;
            }
        }

Answer 3

you should check it->first not it->second .The map is as follows

A=>B ie A mapped to B A in your case is a pair<string,string> and B is a double

 it->first //access A ie access the pair<string,string>
 it->second //access B ie access the double

    if(it->first.first == fn && it->first.second == ln){
            it->second += paid;

Also you are searching for the entry in map which destroys the point of having a map in the first place.

Answer 4

map::insert gives the inserted position or if the key already exists the position of the affected key (second is false). Hence there is no need to search again.