The following code example is taken from the book
C++23 - The Complete Guide
by Nicolai M. Josuttis,
Leanpub, 2026
The code is licensed under a
Creative Commons Attribution 4.0 International License.
// raw code
#include <iostream>
#include <array>
#include <utility>
#include <cstddef> // for std::byte
#include <memory>
#include <memory_resource>
#include <generator>
// coroutine using passed memory resource to hold its state:
std::pmr::generator<long> fibonacci(std::allocator_arg_t,
std::pmr::polymorphic_allocator<>,
int num)
{
// first two numbers are 1:
long a = 1;
long b = 1;
co_yield a; // SUSPEND with first number
co_yield b; // SUSPEND with second number
// loop over sums of previous two numbers:
for (int i = 0; i < num-2; ++i) {
auto sum = a + b;
co_yield sum; // SUSPEND with third to num-th number
a = std::exchange(b, sum);
}
}
int main()
{
// memory pool operating on 1k memory on the stack:
std::array<std::byte, 1'000> buf;
std::pmr::monotonic_buffer_resource pool{buf.data(), buf.size(),
std::pmr::null_memory_resource()};
// call coroutine using the memory pool:
for (auto val : fibonacci(std::allocator_arg, &pool, 10)) {;
std::cout << val << ' ';
}
std::cout << '\n';
}