CODEWITHSUNDEEP
c++unordered-map
mskb
mskb

Reputation: 350

Scope implications when creating unordered_map values within member functions?

I have an unordered_map (as below, as a member of a class) that undergoes a large number of additions and removals of keys. Such additions and removals happen within member functions that have the following strategy. They populate a locally created unordered_map (of the same type as the original member), and finally the keys and the associated vector values are transferred to the class member.

Is this strategy appropriate? Will the scope rules for the locally created unordered_map have an effect on the class member? Thanks for the support!

typedef std::unordered_map<int, std::vector<int> > mapStruct;

class foo {
mapStruct DS;

void f() {
   mapStruct DS_tmp;
   DS_tmp[1].push_back(5);
   DS_tmp[1].push_back(10);
   ...
   ...
   mapStruct::iterator it = DS_tmp.begin();
   while( it != DS_tmp.end() ) {
      DS[it->first] = it->second;
   }
}

};

Upvotes: 0

Views: 215

Answers (1)

Wojtek Surowka
Wojtek Surowka

Reputation: 21003

Nothing in your code stops you from getting rid of DS_tmp and using DS directly in function f. But if due to some reasons you want to first fill temporary local variable and then copy it to the member, you can use swap instead of the while loop (which will never end by the way, because you are not incrementing it):

DS.swap(DS_tmp);

Upvotes: 1

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