CODEWITHSUNDEEP
cmacros
SuperZero
SuperZero

Reputation: 53

Token undeclared error in a macro that does token pasting

I'm not posting the exact code here, but I have tried to represent the problem fully. I have the following macro - 

#define TKN_PST(P) (ABC_##P)

This macro is called in the definition of another macro, which itself is called from another macro as below - 

#define CREATE_TOKEN(P) FURTHER_PROC(P)
#define FURTHER_PROC(X) foo(a, b, TKN_PST(X), ...)

foo() is a function that accepts a variable number of arguments.

I'm getting an error when I call CREATE_TOKEN(P). The compiler tells me that ABC_ is undeclared.

This problem only occurs when I call CREATE_TOKEN(P), and doesn't occur for CREATE_TOKEN(Q), CREATE_TOKEN(R), etc. I suspect that this issue might be the result of P having a definition somewhere in the large code-base.

I tried introducing an extra level of indirection as below - 

#define FURTHER_PROC(X) FURTHER_PROC2(X)
#define FURTHER_PROC2(X) foo(a, b, TKN_PST(X), ...)

Then CREATE_TOKEN(Q), CREATE_TOKEN(R), etc started failing with the error "')' expected before ...".

What might be the reason for this issue?

Upvotes: 1

Views: 123

Answers (1)

SuperZero
SuperZero

Reputation: 53

Thanks to paulsm4 for pointing me in the right direction with his comment above.

I was able to find a definition (#define) for "P" in an included file, which has no replacement text. I hadn't considered this possibility.

Upvotes: 1

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