Checking whether an element exist or not in the map within map

Question

I have a map of the form map > :

For Example: I am storing the intensity value at 2-D co-ordinate(x,y) i

Answer 1

Use std::map::find

auto outerIt = intensityValue.find(x);
if (outerIt != intensityValue.end()) {
    auto innerIt = outerIt->find(y);
    if (innerIt != outerIt->end()) {
        // Do something with the found value
        return;
    }
}
// Didn't return, so it wasn't found

That said, in my experience, using a single map of pairs for this kind of thing is more efficient and easier to use than a nested map. It fits better into standard algorithms and doesn't involve nearly as much tree navigation.

template 
using map2d = std::map, V>;

int main() {
    map2d myMap {
        {{3, 4}, 808.14f},
        {{1, 2}, 333.33f}
    };
    auto it = myMap.find({3, 4});
    if (it != myMap.end()) {
        std::cout << it->second << std::endl;
    }
}