How to fill a C++ container using a (lambda) function?

Question

I want to initialize a container with pointers to objects. I currently have a loop like this:

for(int i=0;i < n;i++) {
    container.push_back(new Object());
}

Which C++ operation (i.e. similar to std::transform) is the right to replace this loop and initialize a container with n newly created objects?

Answer 1

You could use std::generate_n and std::back_inserter with lambda.

std::generate_n(std::back_inserter(container), n, [] { return new Object(); });

Answer 2

Use std::generate:

constexpr int n = 10;
std::vector<Object*> v1(n);
std::generate(v1.begin(), v1.end(), [](){ return new Object(); });

or std::generate_n:

std::vector<Object*> v2;
v2.reserve(n); // pre-allocate sufficient memory to prevent re-allocations
               // (you should have done in original loop approach as well)
std::generate_n(std::back_inserter(v2), n, [] { return new Object(); });