Calling recursive function in push_back - c++

Question

I am writing a function to populate a vector in ascending order using values from a binary search tree. I am also trying to keep the run time of this function to O(n). I am thinking I will need to call a recursive function that traverses the bst and gets the numbers in ascending order. I am confused about how to use the results from the recursive function. Is it okay to use a recursive function inside of push back like this?
void vector_function(){
std::vector<int> *v = new std::vector<int>();
v.pushback(recursive_function(node *p));
}
for example if the Binary Search tree had values 5, 3, 4, 7 the resulting vector would have 3, 4, 5, 7

Answer 1

I am confused about how to use the results from the recursive function. Is it okay to use a recursive function inside of push back like this?
I can think of two ways of doing that.
Option 1
Change recursive_function to also accept a reference to a std::vector<int>. Update its implementation to push_back elements to the vector appropriately.
Pass the vector to recursive_function when calling it.
void recursive_function(node* p, std::vector<int>& v)
{
// When appropriate...
v.push_back(p.data);
}
and use it as
void vector_function(){
std::vector<int> v;
recursive_function(p, v));
}
Option 2
Change recursive_function to also accept a std::function. Update its implementation to call the std::function with the value of the node appropriately. Use a lambda function that can be converted to a std::function that recursive_function accepts in the call to the function. Take care of calling push_back on the vector in the lambda function with the argument passed to it.
void recursive_function(node* p, std::function<void(int)> f)
{
// When appropriate...
f(p.data);
}
and use it as
void vector_function(){
std::vector<int> v;
recursive_function(p, [&v](int e) -> void { v.push_back(e); });
}