# and ## in macros

by

An occurrence of a parameter in a function-like macro, unless it is the operand of # or ##, is expanded before substituting it and rescanning the whole for further expansion. Because g‘s parameter is the operand of #, the argument is not expanded but instead immediately stringified ("f(1,2)"). Because h‘s parameter is not the operand of # nor ##, the argument is first expanded (12), then substituted (g(12)), then rescanning and further expansion occurs ("12").

More Related Contents:

  1. What are the applications of the ## preprocessor operator and gotchas to consider?
  2. How, exactly, does the double-stringize trick work?
  3. Convert a preprocessor token to a string
  4. What does ## mean for the C(C++) preprocessor?
  5. Concatenate int to string using C Preprocessor
  6. Opposite of C preprocessor “stringification”
  7. C Macros to create strings
  8. Macros to create strings in C
  9. #pragma pack effect
  10. Real-world use of X-Macros
  11. Easy way to use variables of enum types as string in C?
  12. Macro definition to determine big endian or little endian machine?
  13. Stringification of a macro value
  14. Are typedef and #define the same in c?
  15. Standard alternative to GCC’s ##__VA_ARGS__ trick?
  16. What are the valid characters for macro names?
  17. Does the C preprocessor strip comments or expand macros first? [duplicate]
  18. Variadic macro trick
  19. Type of #define variables
  20. How to use #if inside #define in the C preprocessor?
  21. #ifdef inside #define
  22. Is there a good reason for always enclosing a define in parentheses in C?
  23. Detecting Endianness
  24. C preprocessor: expand macro in a #warning
  25. C circular dependency
  26. What is a good reference documenting patterns of use of X-Macros in C (or possibly C++)?
  27. Should variable definition be in header files?
  28. How can I implement a dynamic dispatch table in C
  29. Why can’t I use sizeof in a preprocessor condition?
  30. How can I make a char string from a C macro’s value?

Leave a Comment