C2143 syntax error when including boost/optional.hpp
boost, boost-optional, c++, option-type, visual-studio-2015
Solution
I could figure out the reason due to a valuable hint by jv_. I turned on compiler switch `/std:c++latest` in my project settings to be able to use C++17 nested namespace definition feature. Activating this switch removes some deprecated language features, in particular `std::binary_function`, which is still in use in the current Boost distribution (1.62.0), hence producing the compiler error. Finally, I decided to remove the switch `/std:c++latest` (and use the ordinary way to declare my namespaces) and this solved the issue. Thank you all for helping me.
Problem
I'm stuck with a compile-time error which I cannot understand. I try to use `boost::optional` in my code, and as soon as I include `boost/optional.hpp` I cannot build my project any longer. If I comment this include statement out, it works. I don't even have any actual usage of `boost::optional` in my code yet, just the include statement in the class header (see full header below). The compiler error is `C2143 syntax error: missing ',' before '<'` which happens in another Boost header `boost/utility/compare_pointees.hpp` (see GitHub link below). I also successfully use other stuff from Boost like `boost::filesystem::path` in the same project already, so there should be no problem with my Boost distribution as such. Here is my environment: `Microsoft Visual Studio Professional 2015 Version 14.0.25431.01 Update 3` and `boost 1.62.0`. I also use the third-party library C++ REST SDK, everything else is C++ standard library stuff. My header looks like this. I want to add a new method with `boost::optional<size_t>` as return type. ``` #pragma once #include <boost/optional.hpp> // <==== ERROR // C++ REST SDK #define _TURN_OFF_PLATFORM_STRING #include <cpprest/http_listener.h> #include <cpprest/http_msg.h> namespace SANDBOX::REST { class HttpGetHandler { public: virtual void HandleHttpGetRequest(web::http::http_request request) = 0; }; } ``` The place, where the compiler error is reported, is in the Boost header `boost/utility/compare_pointees.hpp`, line 36. You can view the full content of this file on GitHub under https://github.com/boostorg/utility/blob/boost-1.62.0/include/boost/utility/compare_pointees.hpp The compiler output shows nothing more than these messages: ``` 1>D:\dev\lib\boost_1_62_0\boost/utility/compare_pointees.hpp(36): error C2143: syntax error: missing ',' before '<' 1> D:\dev\lib\boost_1_62_0\boost/utility/compare_pointees.hpp(40): note: see reference to class template instantiation 'boost::equal_pointees_t<OptionalPointee>' being compiled 1>D:\dev\lib\boost_1_62_0\boost/utility/compare_pointees.hpp(59): error C2143: syntax error: missing ',' before '<' 1> D:\dev\lib\boost_1_62_0\boost/utility/compare_pointees.hpp(63): note: see reference to class template instantiation 'boost::less_pointees_t<OptionalPointee>' being compiled ========== Build: 0 succeeded, 1 failed, 2 up-to-date, 0 skipped ========== ``` It's surely not a problem of the Boost library. But how can I figure out, what's wrong with my classes or project settings? P.S. I can reproduce the behavior even if I use these most primitive header and source file in my project: Header file `Test.h`: ``` #pragma once #include <boost/optional.hpp> ``` Source file `Test.cpp`: ``` #include "../include/Test.h" ```