I need to satisfy an api function that requires a vector:
void api_function(std::vector<int> vec);
For another reason, I keep values in a
std::map<int,int> map;
Now I need to pass the values of this map to the api_function.
Is there a way to do that without too much space and time overhead, i.e. without iterating through all values or creating a new vector?
No, there isn't. A vector stores its elements contiguously, and the map does not, and so there's no way to create a contiguous arrangement of ints without iterating and copying.
(General algorithms don't operate on containers for that reason, but rather on a more flexible interface like iterators, so that they don't force the user to provide a particular implementation of a range.)
You can do this by using a simple range loop on the map and pushing each value into a vector and then passing that to your function.
Like this:
for (const auto& pair : map)
vector.push_back(pair.second);
If a function asks for vector you are bound to give it a vector. At most, this will help you Copy map values to vector in STL.
As kerrek SB has stated the answer is no. You will need to iterate through your map.
You can do the following to add values to a dynamic vector container. Iterate through the map using std::pair. In this way you're not using a true iterator:
std::vector<int> vec;
for (std::pair<int, int>& e : map) {
vec.push_back(e.second);
}
...
...
api_function(vec); // Invoke function
Finally you can just call your function from your API with your vector.
This will yield a computational time and space complexity of O(n) (with "n" being the number of values you have contained in your map).
You may want to use a map implementation that uses sorted vector internally ('dense map').
