What are C macros useful for?

by

I end up having to remember what the macro is and substitute it in my head as I read.

That seems to reflect poorly on the naming of the macros. I would assume you wouldn’t have to emulate the preprocessor if it were a log_function_entry() macro.

The ones that I have encountered that were intuitive and easy to understand were always like little mini functions, so I always wondered why they weren’t just functions.

Usually they should be, unless they need to operate on generic parameters. 

#define max(a,b) ((a)<(b)?(b):(a))

will work on any type with an < operator.

More that just functions, macros let you perform operations using the symbols in the source file. That means you can create a new variable name, or reference the source file and line number the macro is on.

In C99, macros also allow you to call variadic functions such as printf

#define log_message(guard,format,...) \
   if (guard) printf("%s:%d: " format "\n", __FILE__, __LINE__,__VA_ARGS_);

log_message( foo == 7, "x %d", x)

In which the format works like printf. If the guard is true, it outputs the message along with the file and line number that printed the message. If it was a function call, it would not know the file and line you called it from, and using a vaprintf would be a bit more work.

More Related Contents:

  1. The need for parentheses in macros in C [duplicate]
  2. Overloading Macro on Number of Arguments
  3. C macros and use of arguments in parentheses
  4. Real-world use of X-Macros
  5. Macro definition to determine big endian or little endian machine?
  6. Are typedef and #define the same in c?
  7. What exactly do C include guards do?
  8. Array-size macro that rejects pointers
  9. Opposite of C preprocessor “stringification”
  10. C Macros to create strings
  11. Macro and function with same name
  12. offsetof at compile time
  13. Macros to create strings in C
  14. How to pass arguments in __VA_ARGS to a 2d character array? [closed]
  15. Should I use #include in headers?
  16. How to make a variadic macro (variable number of arguments)
  17. What’s the use of do while(0) when we define a macro? [duplicate]
  18. “#include” a text file in a C program as a char[]
  19. C multi-line macro: do/while(0) vs scope block [duplicate]
  20. Including one C source file in another?
  21. Can gcc output C code after preprocessing?
  22. Why does the C preprocessor interpret the word “linux” as the constant “1”?
  23. C: Expand Macro With Token Pasting
  24. How big can a malloc be in C?
  25. What are the implications of the linux __user macro?
  26. Why does #define not require a semicolon?
  27. Incompatible pointer types passing in _Generic macro
  28. C# Macro definitions in Preprocessor
  29. Are constant C expressions evaluated at compile time or at runtime?
  30. Changing a macro at runtime in C

Leave a Comment