Can a macro call a preprocessor command?
For example, can I write something like,
#define PreProcessor(x, y) #define x ((y)+1)
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No, you cannot. – Peter Oct 01 '16 at 11:54
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1It is not possible to write on the same line the # directive. – BLUEPIXY Oct 01 '16 at 11:55
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Possible duplicate of [Macro-producing macros in C?](http://stackoverflow.com/questions/860273/macro-producing-macros-in-c) – Bo Persson Oct 01 '16 at 14:30
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It is not possible to expand a macro into something that is also a preprocessor directive, as in §6.10.3.4, 3:
The resulting completely macro-replaced preprocessing token sequence is not processed as a preprocessing directive even if it resembles one...
But, it is possible to conditionally define macro itself:
#if CONDITION_A_IS_MET
#define x ((y)+1)
#else
#define x /*...some other definition*/
#endif
Or use an X-macro:
#define PreProcessor(x) X(x, ((x) + 1))
/*...later*/
#define X(a, b) printf("%d, %d", a, b)
PreProcessor(5) /* Outputs 5, 6 */
To cover most of the common cases for that feature.