Path: ...!Xl.tags.giganews.com!local-2.nntp.ord.giganews.com!nntp.brightview.co.uk!news.brightview.co.uk.POSTED!not-for-mail
NNTP-Posting-Date: Sat, 21 Sep 2024 07:35:48 +0000
From: Mark Summerfield <mark@qtrac.eu>
Subject: how to make a macro work as a single line if stmt without braces
Newsgroups: comp.lang.c
MIME-Version: 1.0
User-Agent: Pan/0.149 (Bellevue; 4c157ba)
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Message-ID: <PaWdnZ3R-9zI6nP7nZ2dnZfqn_GdnZ2d@brightview.co.uk>
Date: Sat, 21 Sep 2024 07:35:49 +0000
Lines: 27
X-Usenet-Provider: http://www.giganews.com
X-Trace: sv3-petjQUTKNRd+RoDRUDMJ5vkmUbnQdrtIwVWTh6wq4dBC7KzzRsyhugSq8eRFnNnV+PwCLP1UBJr9Uxz!DY5m2ObI4yfN6etNHy8XVRJCOh7Ov9jk2MJJGJj8rHwoD3qdYRUbpWbsbvQFPlNT8gmxWMoS3aUk!T/FKvzevmruIOPH1aY00eEpq4w==
X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers
X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly
X-Postfilter: 1.3.40
Bytes: 1561

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'