包括boost / optional.hpp时的C2143语法错误 [英] C2143 syntax error when including boost/optional.hpp

问题描述

我遇到了一个我无法理解的编译时错误。我尝试在我的代码中使用 boost :: optional ，并且一旦我包括 boost / optional.hpp I不能再建立我的项目了。如果我评论这个包括语句出来，它的工作原理。我甚至没有任何实际使用 boost :: optional 在我的代码中，只是类头中的include语句（见下面的完整标题）。编译器错误是 C2143语法错误：在另一个Boost头中发生的<'之前缺少'，'before boost / utility / compare_pointees.hpp （参见下面的GitHub链接）。我也成功地使用了其他的东西从Boost像 boost :: filesystem :: path 在同一个项目已经，所以应该没有问题，我的Boost分布。 p>

这里是我的环境： Microsoft Visual Studio Professional 2015版本14.0.25431.01更新3 和 1.62.0 。我还使用第三方库 C ++ REST SDK ，一切都是C ++标准库的东西。

我的标题看起来像这样。我想用 boost :: optional< size_t> 作为返回类型添加一个新方法。

  #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请求）= 0; 
}; 
} 
  

报告编译器错误的位置在Boost标头 boost / utility / compare_pointees.hpp ，第36行。您可以在GitHub上的 https://github.com/boostorg/utility/blob/boost-1.62.0/include/boost/ utility / compare_pointees.hpp

编译器输出只显示以下消息：

  1> D：\dev\lib\boost_1_62_0\boost / utility / compare_pointees.hpp（36）：错误C2143：语法错误：在'<'$之前缺少'，' b $ b 1> D：\dev\lib\boost_1_62_0\boost/ utility / compare_pointees.hpp（40）：note：参考类模板实例化'boost :: equal_pointees_t< OptionalPointee>'正在编译
 1> D ：\dev\lib\boost_1_62_0\boost/ utility / compare_pointees.hpp（59）：错误C2143：语法错误：缺少'，'之前'<'
 1> D：\dev\lib\boost_1_62_0\boost/ utility / compare_pointees.hpp（63）：note：参考类模板实例化'boost :: less_pointees_t< OptionalPointee>'正在编译
 === ======= Build：0 succeeded，1 failed，2 up-to-date，0 skipped ========== 
  

这肯定不是Boost库的问题。但我怎么知道，我的课程或项目设置有什么问题？

即使我在我的项目中使用这些最原始的头文件和源文件，我也可以重现这种行为：

头文件 Test.h ：

  #pragma once 
 
 #include< boost / optional.hpp> 
  

源文件 Test.cpp ：

  #include../include/Test.h
  

解决方案

我可以找出原因，因为一个有价值的提示 jv_ 。我打开编译器开关 / std：c ++ latest 在我的项目设置中能够使用C ++ 17 嵌套命名空间定义功能。激活此开关将删除一些已弃用的语言功能，特别是 std :: binary_function ，它仍然在当前Boost分发（1.62.0）中使用，因此产生编译器错误。最后，我决定删除开关 / std：c ++ latest （并使用普通方式声明我的命名空间），这解决了问题。谢谢大家帮助我。

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"

解决方案

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.

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