CODEWITHSUNDEEP
c++
Prabu
Prabu

Reputation: 1255

Inserting into nested map in C++

Assume I have a nested map of type pointer. Then is there a single line statement to insert into the nested map,

map<int, map<int, int> >* nestedMap;

Currently I am doing this in 2 steps. First creating innermap and then insert into outer map as below,

nestedMap->insert(make_pair(int, map<int, int>)(int, innermap));

If the map is not pointer type, then i can insert easily like this,

nestedMap[int][int] = int;

Is there any simple ways for inserting into nested map of type pointer ?

thanks Prabu

Upvotes: 3

Views: 8649

Answers (4)

user541686
user541686

Reputation: 210455

map::operator[] automatically creates the key/value pair if it doesn't exist.
(That's why it's not const!) So you don't need to create the inner map manually.

If you want to avoid creating the pair automatically, then use map::find() or map::at().

Upvotes: 7

Angew is no longer proud of SO
Angew is no longer proud of SO

Reputation: 171127

I believe the simplest one-liner is:

(*nestedMap)[int][int] = int;

Upvotes: 3

juanchopanza
juanchopanza

Reputation: 227418

access the operator[] via ->:

nestedMap->operator[](5)[6] = 7;

This is analogous to

nestedMap[5][6] = 7;

if nestedMap is not a pointer.

Note that in neither case do you have to explicitly insert a map.

Upvotes: 1

billz
billz

Reputation: 45410

If i understand your question properly, you can actually use reference instead of pointer. You are not having issue with nested map, instead your outter map.

See below code, is what you want?

map<int, map<int, int> >* nestedMap  = new map<int, map<int, int> >;   
map<int, map<int, int> > &nestedMapAlais = *nestedMap;
nestedMapAlais[1][2] = 3;

Upvotes: 1

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