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

On 2024-09-21, Mark Summerfield <mark@qtrac.eu> wrote:

I have this macro:
>
#define WARN(...)                                       \
    do {                                                \
        fprintf(stderr, "%s#%d: ", __FILE__, __LINE__); \
        fprintf(stderr, __VA_ARGS__);                   \
    } while (0);
>
[...]
>
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'

After expansion of the WARN macro there are two semicolons before the 'else'.
The first semicolon is from the

    } while (0);

line, the second is from the

   
    WARN("failed because...");

line.
Removing the semicolon from one of these two lines fixes the compiler error.