Function-like C macro without parentheses

Question

I have encountered the following debug macro in an embedded device codebase:

extern void DebugPrint(uint8_t *s);

#define DEBUG_MSG(x)   do { PRINT_CURRENT_TIME; \
                            DebugPrint x ; } while(0)

Since there are no parentheses around x in the macro body (at the DebugPrint x part), all calls to this macro (all over the codebase) add another set of parentheses around strings:

DEBUG_MSG(("some debug text"));

Is there any reason to do this? Does it simplify optimizing away these calls in release builds, or something like that? Or is it just plain nonsense?

I thought perhaps there would be additional overloads of DebugPrint with more arguments, but there are none.

Answer 1

Here's a theory:

The preprocessor parses the arguments of a macro expansion in a way that mimics the compiler's expression parsing. In particular it parses terms in parentheses as a single argument.

So the DEBUG_MSG author's intention might have been to enforce the use of parentheses.

This might make sense when the DebugPrint print function would actually be a printf style variadic function. You could call the function with a single string literal or with a variable number of arguments:

DEBUG_MSG(("reached this point in code"));

DEBUG_MSG(("value of x = %i", x));

But this is pure speculation. Can't you just ask the author?