问题
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.
回答1:
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,
回答2:
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)
回答3:
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.
回答4:
Sorry, you cannot. You can call other macros in macros but not define new ones.
回答5:
You could try running it through with only the preprocess option, then compiling with the preprocessed file.
回答6:
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.
来源：https://stackoverflow.com/questions/2429240/c-preprocessor-macro-defining-macro