Re: how to make a macro work as a single line if stmt without braces

On 21/09/2024 08:35, Mark Summerfield wrote:

I have this macro:
 #define WARN(...)                                       \
     do {                                                \
         fprintf(stderr, "%s#%d: ", __FILE__, __LINE__); \
         fprintf(stderr, __VA_ARGS__);                   \
     } while (0);
 which I use like this:
 total++;
if (failed) {
     WARN("failed because...");
} else
     ok++;
 I would prefer to be able to write this instead:
 total++;
if (failed)
     WARN("failed because...");
else
     ok++;
 but doing so results in a compiler error:
 error: 'else' without a previous 'if'

Remove the semicolon at the end of the macro.
As it is, it compiles to:
  if (failed) do {...} while 0;; else ok++:
There are two semicolons together, the second terminates the whole if statement, leaving an open 'else'.