Why compiler complain about this macro declaration

Question

I write the following macro for debug convinience,

1 #ifndef DEF_H
2 #define DEF_H
3 #define DEBUG_MODE
4 #define DEBUG_INFO(message)     \\
5         #ifdef         


        

Answer 1

You can't embed a preprocessor directive in another preprocessor directive (the #ifdef DEBUG_MODE inside the definition of DEBUG_INFO). Instead, do something like

#ifdef DEBUG_MODE
# define DEBUG_INFO(message) cout << message << endl
#else
# define DEBUG_INFO(message) 0
#endif

(This is still not ideal; defensive macro coding suggests something like

#ifdef DEBUG_MODE
# define DEBUG_INFO(message) do {cout << message << endl;} while (0)
#else
# define DEBUG_INFO(message) 0
#endif

Perhaps an inline function would work better.)

Answer 2

You cannot have #ifdefs inside a macro definition. You need to turn it inside out:

#ifdef DEBUG_MODE
#define DEBUG_INFO(message) cout << (message) << endl
#else
#define DEBUG_INFO(message)
#endif

Answer 3

I geuss if you eat '\' at line 7, the piece of Code will work.