ambiguous overload for ‘operator<<' Error.

[kafi350]

I am facing this error after including vexcl. Even if i specify the backend it shows the error.

include <vexcl/vexcl.hpp>

    ```

from /home/kafi/Documents/Projects/CODD-pro-lib_integration/main.cpp:14: /usr/include/boost/date_time/date_generators.hpp: In member function ‘virtual std::string boost::date_time::nth_kday_of_month::to_string() const’: /usr/include/boost/date_time/date_generators.hpp:237:8: error: ambiguous overload for ‘operator<<’ (operand types are ‘std::basic_ostream’ and ‘int’) 236	ss << 'M'	~~~~~
std::basic_ostream
237	<< staticcast(month) << '.'
^~ ~~~~~~~~
int

In file included from /usr/include/c++/9/iterator:64, from /usr/include/CL/cl.hpp:219,

[ddemidov]

I can not reproduce this with g++ 11. The following compiles for me:

#include <vexcl/vexcl.hpp>

int main() {
    std::cout << 'M' << std::endl;
}