std::map vs. vector of vector

Question

I need a container to store a value (int) according to two attributes, source (int) and destination (int) i.e. when a source sends something to a destination, I need to store it

Answer 1

I need a container to store a value (int) according to two attributes, source (int) and destination (int)

std::map, int>

A subsequent process needs to check this container, to see if an element exists in for a particular source, and a particular destination - it will need to differentiate between an empty 'space' and a filled one.

std::map::find

http://www.cplusplus.com/reference/map/map/find/

The container has the possibility of being very sparse.

Use a std::map. The "correct" choice of a container is based on how you need to find things and how you need to insert/delete things. If you want to find things fast, use a map.