Question

Everybody,
I am a Python/C# guy and I am trying to learn C++.
In Python I used to do things like:
myRoutes = {0:[1,2,3], 1:[[1,2],[3,4]], 2:[[1,2,3],[[1,2,3],[1,2,3]],[4]]}

Basically when you have arrays of variable length and you don’t want to wast a 2D matrix for them, nesting arrays into a dictionary to keep track of them is a good option.

In C++ I tried std::map<int, std:map<int, std:map<int, int> > > and it works but I feel there got to bo a better way to do this.

I prefer to stick to the standard libraries but popular libraries like boost are also acceptable for me.

I appreciate your help,
Ali

Answer 1

Many of us share the pain you’re experiencing right now but there are solutions to them. One of those solutions is the Boost library (it’s like the 2nd standard library of C++.) There’s quite a few collection libraries. In your case I’d use Boost::Multi-Dimentional Arrays.

Looks like this:

boost::multi_array<double,3> myArray(boost::extents[2][2][2]);

Which creates a 2x2x2 array. The first type in the template parameters “double” specifies what type the array will hold and the second “3” the dimension count of the array. You then use the “extents” to impart the actual size of each of the dimensions. Quite easy to use and syntatically clear in its intent.

Now, if you’re dealing with something in Python like foo = {0:[1,2,3], 1:[3,4,5]} what you’re really looking for is a multimap. This is part of the standard library and is essentially a Red-Black tree, indexed by key but with a List for the value.