19.4 do while(0)

[Lundin]

I would recommend the committee to rephrase rule 19.4 so that it does not allow do-while-zero inside function-like macros.

The do-while-zero mechanism has only two purposes:

Code:

/* "goto wrapper" */
do
{
  if(something)
  {
    break;
  }
  ...
} while(0);

The above code is a "hack" to stay compliant with rule 14.4 (goto shall not be used). But it surely leads to even less readable code than goto does.

Code:

/* "if-statement fiasco saver" */
#define FUNC(x) do
{
  do_this();
  do_that();
} while(0)  /* no semicolon here, as enforced by 19.4 */

if(something)
  FUNC(X); /* the macro allows the semicolon to be placed here */
else

The above is a "hack" that only applies to code non-compliant to rule 14.9 (if shall be followed by a compound statement). The sole purpose of do-while-zero is to save non-compliant code from the compiler errors it would otherwise receive! If the macro was written as two braces without the do while, there would be a compiler error because of the semicolon.

To sum this up: if code is to conform with (required) rules 14.4 and 14.9, then there is no reason for rule 19.4 to allow do-while-zero.