how to combine multiline macros in C with comments at the end of a line

Question

I'm having a brain cramp... is there a way in C to combine a multiline macro with a comment at each line?

e.g.

#define MYARRAY { \
  0.001,   //  5 mV \
  0.002,   // 10 mV \
  0.004,   // 20 mV \
  0.007,   // 35 mV \
  0.013    // 65 mV \
}

I need to define a list of commented array values in a header file that gets used elsewhere, and make it very human-readable.

Answer 1

You can use multiline comments as a way to continue macro definitions from one line to another, instead of backslashes. As described in the C standard, §5.1.1.2/1, comments are reduced to a single space during translation phase 3, while preprocessing directives are executed in phase 4. In effect, that means that newline characters inside a multiline comment do not terminate a preprocessing directive, so you could write:

#define MYARRAY { /*
*/   0.001,   /*  5 mV 
*/   0.002,   /* 10 mV
*/   0.004,   /* 20 mV
*/   0.007,   /* 35 mV
*/   0.013    /* 65 mV
*/ }

Note that line continuations (backslash newline) are removed in phase 2, before comments are recognized as such. So the problem with using C++-style // comments is not that the comment includes the backslash; rather it is that the lines are first concatenated and then the comment extends to the end of the concatenated lines.