Map of Maps

[ami]

Hello everyone,

I have a map of maps :-

typedef map <string, map <string, int> > myMapofMaps;
myMapofMaps a;

I'm trying to insert an entry but without actually creating the inner map as an object. Is that possible at all ?

In other words, I want to do something like :-

a.insert(pair <string, map <string, int> >("AAA",(pair <string, int> ("A1", 1))));

As you can see in the inner map I'm not specifying the map name.

I need to do this this way because I don't know in advance how many inner maps there will be, so I cannot do :-

map <string, int> x1;
map <string, int> x2;
map <string, int> x3;
etc.

I need the compiler to know that once I insert an entry to the outer map, then an inner map needs to be created automatically and I need to be able to access it later.

I tried putting the inner map into a vector, but I still cannot make_pairs this way. I still need to find a way of inserting to a map without actually manually creating it myself.

Does this make sense ? Can I let the compiler create maps for me at run time?

Many thanks for your help.

[drkybelk]

with std::map you can do sth like

map<string,int> myMap1;
myMap1["entry in first Map"] = 1;

map<string, map<string,int> > myMap2;
myMap2["entry in second Map"]/* = map<string,int>()*/; // the commented out stuff is not needed, the [..] operator insert a default element anyway

But if you want to add any other than the default element, I would create a little function that returns a map<string,int> object.

map<string,int> createElement(string s, int i)
{
    map<string,int> reval;
    reval[s] = i;
    return reval;
}
// now you can:
myMap2["'nother entry"] = createElement("innerMapKey",42);

Dunno whether this is any good to you...

[ami]

Many thanks for that.

Can you please tell me how would you insert into the map created in createElement ? I mean, as I was saying prior to Run time, I don't know in advance how many map<string,int> maps there will be, so how I can name them ? I mean, we normally do :-

map<string,int> a1;
map<string,int> a2;

and from what I understand you are suggest doing :-

map<string,int> newMap = createElement(...);

but the point is, I cannot hard-code "newMap" as I don't know in advance ghow many maps I want to create. Should I do it with a class that returns the map you're suggesting and then do: new createElement(...) ?

If so, will a pointer to this class return me the "right map" every time ?

Many thanks.

[k_alex]

Can't you do something like this:

  typedef map <string, map <string, int> > myMapofMaps;
  myMapofMaps a;
  a["AAA"]["A1"] = 10; 
  a["AAA"]["A2"] = 20;
  a["AAA"]["A3"] = 20;
  a["BBB"]["B1"] = 10;
  //... etc

This code will create as many inner maps as you need.

[ami]

Many thanks.

I just didn't see the obvious...

Thanks again.