CODEWITHSUNDEEP
c++dictionaryiteratornested
AnthonyW
AnthonyW

Reputation: 1998

Pulling values from nested maps

Looked around SO and couldn't find quite what I needed. I am looking for a way to pull the key from the outside map and the value from the inside map for usin in an output statement. If I had one map I know I can pull the data I need from the inside map by using insideMap[key]. However, the [] operator does not seem to work in this implementation ((*itr).second)[keyword].

map< string, map<string, int> >::const_iterator itr; 
for( itr=books.begin(); itr!=books.end(); ++itr)
  //code I need here

Upvotes: 1

Views: 1299

Answers (2)

bjhend
bjhend

Reputation: 1713

You can use std::map::at() instead of operator[]. at() returns the value of a key like operator[], but there is a const version of at().

(itr->second).at(keyword)

The difference between at() and operator[] is that at() does an additional range check and throws an out_of_range exception if it fails.

Upvotes: 1

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726579

The problem with [] is const-ness of your iterator: the [] operator is not const, so you need to use find(keyword) instead, and dereference the iterator that it returns:

*(((*itr).second).find(keyword))

You could also switch to non-const iterator and use [].

Upvotes: 1

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