Question

To try out the new coroutine feature in boost I created the following program:

#include <boost/coroutine/all.hpp>
#include <string>
#include <vector>


typedef boost::coroutines::coroutine<int(char)> coroutine_t;


void f(coroutine_t::caller_type & ca)
{
    std::vector<int> vec = {1, 2, 3};
    for (int i : vec)
    {
        char c = ca.get();
        std::cout << "c: " << c << std::endl;
        ca(i);
    }
}

int main()
{
    coroutine_t cr(f);
    std::string str("abc");
    for (char c : str)
    {
        std::cout << c << std::flush;
        cr(c);
        int n = cr.get();
        std::cout << n << std::endl;        
    }
}

The code is based on the sample code from the docs.

My build command goes as follows:

$ g++ -std=c++11 -o test -I/usr/local/include -L/usr/local/lib main.cpp /usr/local/lib/libboost_context.a

Output:

$ ./test
test: /usr/local/include/boost/coroutine/detail/coroutine_get.hpp:43: typename boost::coroutines::detail::param<Result>::type boost::coroutines::detail::coroutine_get<D, Result, arity>::get() const [with D = boost::coroutines::coroutine<char(int), 1>; Result = char; int arity = 1; typename boost::coroutines::detail::param<Result>::type = char]: Assertion `static_cast< D const* >( this)->impl_->result_' failed.
Aborted (core dumped)

The program is aborted due to failed assertion. Can you help me find the error in my code?

Answer 1

I believe you need to add a call ca() at the beginning of your function f.

From the boost documentation:

The execution control is transferred to coroutine at construction (coroutine-function entered) – when control should be returned to the original calling routine, invoke boost::coroutines::coroutine<>::operator() on the first argument of type boost::coroutines::coroutine<>::caller_type inside coroutine-function.