Is this the defined behavior?

Question

I have made a macro:

#define QUEUE_SEND_STATUS(x) ( (x == 0) ? printf("Fail\n") : printf("Success\n"))

It works as expected. But, my question is is that is this behavior defined in C? Can function calls be used in MACROS?

Thanks!

Answer 1

Yes, this code has well-defined behavior. However, there are some ways it could be improved.

• Function-like macro parameters should be surrounded by parenthesis whenever used, to prevent operator precedence bugs: ((x) == 0). (The check vs zero is actually superfluous, you could as well just type (x) ?)

• You can use the printf calls inside the ?: operator only because they have the same/compatible return types. In case they were different functions with different return types, it wouldn't be possible.

• The whole thing could be rewritten as:

  #define QUEUE_SEND_STATUS(x) puts((x) ? "Fail" : "Success").