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POHow can I guarantee full macro expansion of a parameter before paste?
 

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  1. POHow can I guarantee full macro expansion of a parameter before paste?
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    <p>I have a general macro:</p> <pre><code>#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 </code></pre> <p>how do I guarantee that the variable <code>Case</code> is fully expanded before it gets pasted in <code>mSwitch</code>?</p> <p>It works fine if <code>mSwitch</code> 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.</p> <p>I'm using <code>MSVC 2005</code>.</p> <p>Is there a simple way to make sure a parameter is fully expanded before pasting is done?</p> <p>Thanks</p> <hr> <p>well, it isn't that hard to give an example maybe:</p> <pre><code> #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] </code></pre> <p>this is debug code that has no problems recursively parsing nested expressions like:</p> <pre><code>DebugInfo( BInt( BNot( IAdd(4,BNot(IAdd(6,7)) ) ) ) ); " </code></pre> <p>which yields:</p> <pre><code>"[BInt:1]( [BNot:1]( [IAdd:2]( [Dig:4], [BNot:1]( [IAdd:2]( [Dig:6], [Dig:7] ) ) ) ) )" </code></pre> <p>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.</p>
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    1. USVonRiphenburger
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    1. COEssentially a duplicate of [SO 1489932](http://stackoverflow.com/questions/1489932/c-preprocessor-and-concatenation/]
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      1. POHow can I guarantee full macro expansion of a parameter before paste?
      1. USJonathan Leffler
 

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