CODEWITHSUNDEEP
gccc-preprocessor
Mike
Mike

Reputation: 60743

C preprocessor Macro defining Macro

Can you do something like this with a macro in C?

#define SUPERMACRO(X,Y) #define X Y

then

SUPERMACRO(A,B) expands to #define A B

I have a feeling not because the preprocessor only does one pass.

Official gcc only. No third-party tools please.

Upvotes: 58

Views: 42453

Answers (6)

user2096143
user2096143

Reputation:

You might do this though: #define SUPERMACRO(X,Y) define X Y

Then you can use your editors macro-expansion functionality and paste in the missing #.

Or even better: Use a different, more powerful string-processing language as your preprocessor.

Upvotes: -2

user922475
user922475

Reputation:

You could try running it through with only the preprocess option, then compiling with the preprocessed file.

Upvotes: 1

WhirlWind
WhirlWind

Reputation: 14112

You cannot define macros in other macros, but you can call a macro from your macro, which can get you essentially the same results.

#define B(x) do {printf("%d", (x)) }while(0)
#define A(x) B(x)

so, A(y) is expanded to do {printf("%d", (y)) }while(0)

Upvotes: 20

John Bode
John Bode

Reputation: 123458

No. The order of operations is such that all preprocessor directives are recognized before any macro expansion is done; thus, if a macro expands into something that looks like a preprocessor directive, it won't be recognized as such, but will rather be interpreted as (erroneous) C source text.

Upvotes: 4

Michael Burr
Michael Burr

Reputation: 340168

Macros can't expand into preprocessing directives. From C99 6.10.3.4/3 "Rescanning and further replacement":

The resulting completely macro-replaced preprocessing token sequence is not processed as a preprocessing directive even if it resembles one,

Upvotes: 41

Tuomas Pelkonen
Tuomas Pelkonen

Reputation: 7821

Sorry, you cannot. You can call other macros in macros but not define new ones.

Upvotes: 3

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