Compile Error In visual studio 2017

[runner66]

as document said "It requires C++14 and the Boost Libraries 1.67.0 or later.", but when comiple in VS （with boost1.68+cpp14）, I get serveal errors.
boost_1_68_0\boost\variant\detail\make_variant_list.hpp(40): error C2977: “boost::mpl::list”:
boost_1_68_0\boost\variant\detail\make_variant_list.hpp(40): error C2955: “boost::mpl::list”:

Only when I define MQTT_STD_VARIANT with cpp17, I can compile sucess.

[redboltz]

On clang++ (13.0.1) -std=c++14, Boost 1.78.0, MQTT_STD_VARIANT=OFF cmake option (MQTT_STD_VARIANT preprocessor macro is not defined), no errors are reported.
C2977 means too many template arguments.

mqtt_cpp/include/mqtt/config.hpp

Lines 12 to 29 in f1ebfbf

	// Use boost variant
	// user intentionally defined BOOST_MPL_LIMIT_LIST_SIZE but size is too small
	// NOTE: if BOOST_MPL_LIMIT_LIST_SIZE is not defined, the value is evaluate as 0.
	#if defined(BOOST_MPL_CFG_NO_PREPROCESSED_HEADERS) && BOOST_MPL_LIMIT_LIST_SIZE < 40
	#error BOOST_MPL_LIMIT_LIST_SIZE need to greator or equal to 40
	#else // defined(BOOST_MPL_CFG_NO_PREPROCESSED_HEADERS) && BOOST_MPL_LIMIT_LIST_SIZE < 40
	// user doesn't define BOOST_MPL_LIMIT_LIST_SIZE intentionally
	// but the defult value could be defined
	#undef BOOST_MPL_LIMIT_LIST_SIZE
	#define BOOST_MPL_CFG_NO_PREPROCESSED_HEADERS
	#define BOOST_MPL_LIMIT_LIST_SIZE 40
	#endif // defined(BOOST_MPL_CFG_NO_PREPROCESSED_HEADERS) && BOOST_MPL_LIMIT_LIST_SIZE < 40

mqtt_cpp set to the limit list size to 40 if it is not defined.

Those information might help you to analyze the problem.

[redboltz]

Perhaps, insert

#include <mqtt/variant.hpp>

into the top of your source code (cpp file) might solve the error.

If it is solved please let me know the current include information.

[runner66]

Yes, It works. ths
a little weird...

[runner66]

another puzzle, what's the difference mqtt_cpp-12.0.0 and mqtt_cpp-master?
seems code is not absolutly the same

[redboltz]

Yes, It works. ths a little weird...

Oh really, I need your source code (mqtt_cpp include part) to fix the issue. So far, I only know the error code. I cant't fix it.

Maybe

mqtt_cpp/include/mqtt/client.hpp

Line 10 in f1ebfbf

#include <mqtt/variant.hpp> // should be top to configure variant limit

mqtt_cpp/include/mqtt_client_cpp.hpp

Line 7 in f1ebfbf

#include <mqtt/config.hpp> // should be top to configure boost::variant limit

are related.

[redboltz]

another puzzle, what's the difference mqtt_cpp-12.0.0 and mqtt_cpp-master? seems code is not absolutly the same

You can compare by yourself
v12.0.0...master

[runner66]

Ok, ths.
I try to compile the same code in Linux OS with vscode, but get a lot of errors, any tips?

mqtt/will.hpp:47:23: error：enclosing class of constexpr non-static member function ‘mqtt::buffer& mqtt::will::topic()’ is not a literal type
constexpr buffer& topic() {
^
mqtt/will.hpp:50:29: error：enclosing class of constexpr non-static member function ‘const mqtt::buffer& mqtt::will::message() const’ is not a literal type
constexpr buffer const& message() const {
^
mqtt/will.hpp:53:23: error：enclosing class of constexpr non-static member function ‘mqtt::buffer& mqtt::will::message()’ is not a literal type
constexpr buffer& message() {
^
mqtt/will.hpp:56:22: error：enclosing class of constexpr non-static member function ‘mqtt::retain mqtt::will::get_retain() const’ is not a literal type
constexpr retain get_retain() const {
^
mqtt/will.hpp:59:19: error：enclosing class of constexpr non-static member function ‘mqtt::qos mqtt::will::get_qos() const’ is not a literal type
constexpr qos get_qos() const {
^
mqtt/will.hpp:62:37: error：enclosing class of constexpr non-static member function ‘const properties& mqtt::will::props() const’ is not a literal type
constexpr v5::properties const& props() const {
^
mqtt/will.hpp:65:31: error：enclosing class of constexpr non-static member function ‘mqtt::v5::properties& mqtt::will::props()’ is not a literal type
constexpr v5::properties& props() {