CODEWITHSUNDEEP
c++listdictionary
user1594047
user1594047

Reputation: 181

default value of a list used as map value

Hi I was wondering if I have a map with int as element and list of int as value and I try to access to a key which is not in the map. The operator return a default value. But what is suppose to be a default value for a list ? the default constructor ?

Upvotes: 2

Views: 75

Answers (2)

JBentley
JBentley

Reputation: 6260

Yes, it will default construct a list. See here.

If this is not the behaviour you want, you can use std::map::at (see here) instead of std::map::operator[] to access elements, which will throw an exception if the key doesn't exist, rather than inserting a new element.

Note: my answer assumes that you were referring to the std namespace in your question.

Upvotes: 3

Shafik Yaghmour
Shafik Yaghmour

Reputation: 158479

If the key is not in the map than operator [] inserts a new element with that key and uses the default constructor, which you can read more about here

The default constructor for std::list constructs an empty container.

Upvotes: 1

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