如何保证粘贴前参数的完整宏扩展?

How can I guarantee full macro expansion of a parameter before paste?(如何保证粘贴前参数的完整宏扩展?)

问题描述

我有一个通用宏:

#define mSwitch( Root, Case )  Root##_Case_##Case

#define mSpecialDisplay( what, Val )  mSwitch(mSpecialDisplay,what)(Val)
#define mSpecialDisplay_Case_Int(Val)    ...do stuff
#define mSpecialDisplay_Case_Float(Val)  ...do stuff
...more special cases

如何保证变量 Case 在粘贴到 mSwitch 之前完全展开?

how do I guarantee that the variable Case is fully expanded before it gets pasted in mSwitch?

如果向 mSwitch 传递一个文字值，它会正常工作，但如果有多层间接或中间操作，mSwitch 最终会在它们完全展开之前粘贴其中一层.

It works fine if mSwitch is passed a literal value, but if there are several layers of indirection, or intermediary operations, mSwitch ends up pasting one of those before they get fully expanded.

我正在使用 MSVC 2005.

有没有一种简单的方法可以确保参数在粘贴完成之前完全展开?

Is there a simple way to make sure a parameter is fully expanded before pasting is done?

谢谢

好吧，举个例子也许并不难:

well, it isn't that hard to give an example maybe:

  #define mMDebugInfo( ... ) mMDebugExp( mMDebugInfo_( 0, __VA_ARGS__ ) )

  #define mMDebugInfo_( C, ... ) mMAritize( mMSwitch( mMDebugInfo, mMMetaTrait( Detect, __VA_ARGS__ ) ), (C, __VA_ARGS__) )

  #define mMDebugInfoRep( C, ... ) mMXP##C( mMDebugInfo_ )mMXP##C((mMIInc(C),__VA_ARGS__)) //(mMExpDo(mMGlue( mM, C)##DebugInfo_(mMIInc(C),__VA_ARGS__))

  #define mMDebugInfo1( C, ... ) mMAritize( mMSwitch( mMDebugInfo, mMMetaTrait( Detect, __VA_ARGS__ ) ), (mMIInc(C), __VA_ARGS__) )

  #define mMDebugInfo_Case_Nil(...) [Nil]

  #define mMDebugInfo_Case_CntArgs(C,I,...) 
mMDebugInfoRep(C,I),mMDebugInfoRep(C,__VA_ARGS__)
  #define mMDebugInfo_Case_PrnNull(C,I) [()]

  #define mMDebugInfo_Case_Prn(C,I)   ( mMDebugInfoRep(C,mMDPrn(I)) )

  #define mMDebugInfo_Case_ActFn(C,I) mMAritize( mMDebugInfo_Case_Fn, (C, I, mMTrait_Fn_mM##I) )

  #define mMDebugInfo_Case_PassFn(C,I) mMAritize( mMDebugInfo_Case_Fn, (C, mMTrait_Fn_mM##I) )

  #define mMDebugInfo_Case_Fn( C,Name, Reg, ArgCnt, PArgs ) [Name:ArgCnt]( mMAritize( mMSwitch( mMDebugInfo_Case_Fn, ArgCnt ), (C, mMDPrn( PArgs ) )) )

  #define mMDebugInfo_Case_Fn_Case_V(C, _1, ...) mMDebugInfoRep(C, _1), mMDebugInfoRep(C, __VA_ARGS__)

  #define mMDebugInfo_Case_Fn_Case_0(...) [Nil]

  #define mMDebugInfo_Case_Fn_Case_1(C, _1, ...) mMDebugInfoRep(C, _1)

  #define mMDebugInfo_Case_Fn_Case_2(C, _1, _2, ...) mMDebugInfoRep(C, _1), mMDebugInfoRep(C, _2)

  #define mMDebugInfo_Case_Fn_Case_3(C, _1, _2, _3, ...) mMDebugInfoRep(C, _1), mMDebugInfoRep(C, _2), mMDebugInfoRep(C, _3)  

  #define mMDebugInfo_Case_Fn_Case_4(C, _1, _2, _3, _4, ...) mMDebugInfoRep(C, _1), mMDebugInfoRep(C, _2), mMDebugInfoRep(C, _3), mMDebugInfoRep(C, _4)

  #define mMDebugInfo_Case_Int(C,I)   [Num:I]

  #define mMDebugInfo_Case_Digit(C,I) [Dig:I] 

  #define mMDebugInfo_Case_Bool(C,I)  [Bin:I]

  #define mMDebugInfo_Case_CCode(C,I) [CCd:I]

  #define mMDebugInfo_Case_UToken(C,I) [UT:I]

这是在递归解析嵌套表达式时没有问题的调试代码，例如:

this is debug code that has no problems recursively parsing nested expressions like:

DebugInfo( BInt( BNot( IAdd(4,BNot(IAdd(6,7)) ) ) ) ); 
"

产生:

"[BInt:1]( [BNot:1]( [IAdd:2]( [Dig:4], [BNot:1]( [IAdd:2]( [Dig:6], [Dig:7] ) ) ) ) )"

示例表达式中的宏函数处于非活动形式.当我激活表单时，问题就出现了 - 各个参数的解析链可能会变得任意长，并且在使用之前它们没有得到完全解决.

The macro functions in the example expression are in inactive form. The problem is happening when I activate the form - the parse chain for the individual arguments can get arbitrarily long and they aren't getting resolved completely before they are getting used.

推荐答案

这是通常的成语:

#define mSwitch(Root, Case) mSwitch_(Root, Case)
#define mSwitch_(Root, Case) Root##_Case_##Case

C 预处理器宏的所有参数都在宏本身展开之前完全展开，除非 # 或 ## 运算符应用于他们；然后他们没有扩大.因此，要在 ## 之前获得完全扩展，您可以通过不使用 ## 的包装宏传递参数.

All of the arguments to a C preprocessor macro are fully expanded before the macro itself is expanded, unless the # or ## operator is applied to them; then they're not expanded. So to get full expansion before ##, you pass the arguments through a wrapper macro that doesn't use ##.

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