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c++qtqmap

Does QMap support custom comparator functions?

I couldn't find a way to set a custom comparator function for QMap, like I can for std::map (the typename _Compare = std::less<_Key> part of its template arguments).

Does QMap have a way to set one?

Solution

  • It's not documented (and it's a mistake, I think), but in you can specialize the qMapLessThanKey template function for your types (cf. the source). That will allow your type to use some other function rather than operator<:

    template<> bool qMapLessThanKey<int>(const int &key1, const int &key2) 
{ 
    return key1 > key2;  // sort by operator> !
}

    Nonetheless, std::map has the advantage that you can specify a different comparator per each map, while here you can't (all maps using your type must see that specialization, or everything will fall apart).