英文:
How to skip a C++ preprocessor directive in C#
问题
以下是您要翻译的内容：
我试图在C++和C#中使用相同的类。我正在使用预处理器指令来处理代码差异。然而，即使它们位于#if #endif部分中，我也无法跳过C++指令（如#include或#define）。
以下代码在C++中编译，但在C#中不编译：
#if !NET
#pragma once
#include <string> //<-- C# error CS1024: Preprocessor directive expected
#define public public: //<-- C# error CS1025: Single-line comment or end-of-line expected
#endif
#if NET
namespace A.B {
#else
namespace A::B {
using namespace std;
#endif
class C {
string str;
public C() {str = "test";}
};
}
#if !NET
#undef public
#endif
问题：
- 为什么我不能这样做？
- 为什么C#预处理器尝试理解位于#if !NET部分内的#include或#define指令？
- 有没有办法做到这一点？
编辑：
哎呀！重新阅读C#标准规范的第6.5.5章，我注意到以下段落：
> 剩余的条件部分将被跳过，源代码中不会生成任何标记，除了那些用于预处理指令的标记。因此，跳过的源代码，除了预处理指令外，在词法上可能是不正确的。跳过的预处理指令必须在词法上正确，但不会被其他方式处理。在正在跳过的条件部分中，任何嵌套的条件部分（包含在嵌套的#if...#endif结构中）也将被跳过。
- 所以，好的，我的第一个问题得到了答案。
- 第二个问题呢：为什么预处理指令必须在词法上正确？
- 不过，有人知道如何避免这个限制吗？如何使上述代码工作？
英文:
I am trying to use the same class in C++ and C#. I am using preprocessor directives to scape code differences. However, I cannot skip C++ directives (as #include or #define) even when they are inside an #if #endif section.
The following code compiles in C++, but not in C#:
#if !NET
#pragma once
#include <string> //<-- C# error CS1024: Preprocessor directive expected
#define public public: //<-- C# error CS1025: Single-line comment or end-of-line expected
#endif
#if NET
namespace A.B {
#else
namespace A::B {
using namespace std;
#endif
class C {
string str;
public C() {str = "test";}
};
}
#if !NET
#undef public
#endif
Questions:
- Why can I not do this?
- Why C# preprocessor tries to understand
#includeor#definedirectives if they are inside an#if !NETsection? - Is there anyway to do it?
EDIT:
Ouch! Rereading chapter 6.5.5 of the C# standard specification, I notice the following paragraph:
> Any remaining conditional sections are skipped and no tokens, except those for pre-processing directives, are generated from the source code. Therefore skipped source code, except pre-processing directives, may be lexically incorrect. Skipped pre-processing directives shall be lexically correct but are not otherwise processed. Within a conditional section that is being skipped any nested conditional sections (contained in nested #if...#endif constructs) are also skipped.
- So, ok, my first question is answered.
- What about the second one: Why pre-processing directives shall be lexical correct?
- However, does anybody know how to avoid this limitation? How to make the above code work?
答案1
得分: 0
终于，我找到了一种使用两个文件解决这个问题的方法：
注意： 这可能不是最佳的想法，但我找不到比这更好的方法。
/*** myfile.hpp ***/
#pragma once
#include <string>
#define public public:
#include "myfile.cs"
#undef public
/*** myfile.cs ***/
#if NET
namespace A.B {
#else
namespace A::B {
using string = std::string;
#endif
class C {
string str;
public C() {str = "test";}
};
}
使用这两个文件，C++ 中应该包括myfile.hpp，而在C#中只需要myfile.cs。
这个想法来自于这里：https://stackoverflow.com/a/56839291/13087883
英文:
Finally, I have found a method to solve this issue using two files:
Note: It may not be the best idea, but I can't find a better one than this.
/*** myfile.hpp ***/
#pragma once
#include <string>
#define public public:
#include "myfile.cs"
#undef public
/*** myfile.cs ***/
#if NET
namespace A.B {
#else
namespace A::B {
using string = std::string;
#endif
class C {
string str;
public C() {str = "test";}
};
}
With these two files, on C++ myfile.hpp should be included, and on C# only myfile.cs is needed.
The idea is taken from here: https://stackoverflow.com/a/56839291/13087883
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