I don't know what I did wrong but I have a map:
std::map<std::pair<ID, ID>, std::queue<Datum>> readQueues;
Everything's fine until I call readQueues[std::make_pair(src, dst)]; and then I get an error that my arguments do not match the arguments of the function. The funny thing is that the whole thing works with std::map::find and map::at with the exact same arguments... Any ideas?
The subscript-operator of map cannot work for const maps (or const references to maps for that matter). That is because it may actually change the map - recall that
m[a] = 7;
will work even if a is not present in m. In that case a is inserted in to m first. Thus the semantic involves a potential modification, and that is exactly what const member functions shall not do.
You can instead use find which will return an iterator. In particular, find returns end() when the passed key is not contained yet.
The operator[] is non-const, so you cannot use it when you only have a const-reference to your map, unlike find and at.
[]-operator inserts new elements into the map.
srcanddst?