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From: flaps@utcsri.UUCP
Newsgroups: comp.lang.c
Subject: Style question re common C expression.
Message-ID: <4934@utcsri.UUCP>
Date: Mon, 15-Jun-87 01:18:39 EDT
Article-I.D.: utcsri.4934
Posted: Mon Jun 15 01:18:39 1987
Date-Received: Tue, 16-Jun-87 00:38:40 EDT
Reply-To: flaps@utcsri.UUCP (Alan J Rosenthal)
Distribution: world
Organization: University of Toronto
Lines: 49


Frequently I write expressions of the form "x ? x : y".  For example,
in unix where "getenv" returns an environment variable, I might have
something like:
	char *t;
	execl((t = getenv("EDITOR")) ? t : "/bin/ed",file,(char *)NULL);
to run the user-specified editor, with a default of /bin/ed.

My complaint about this syntax is mostly about having to use the
temporary variable.  I know assembler-level optimizers will elide it,
but the point is that there is actually no operations happening
conceptually between the '?' and the ':' and I don't think I should
have to specify them.

I think that "getenv("EDITOR") ? : "/bin/ed"" should do what I mean
here.  Unfortunately this is not supported; also, the expression
"getenv("EDITOR") || "/bin/ed"" doesn't work because the value of the
getenv is converted to 1 or 0.

Also, in my current large project, for example, I have some functions
which can accept pointers or NULLs for return values: for example,

	void f(ip)
	int *ip;
	{
	    int trash;
	    ...
	    *(ip ? ip : &trash) = something;

The same syntax applies here.  (This can't be converted to an if
statement because actually the pointer is passed to another function
which dereferences it.)

So the main question is, is there some nice way I missed to specify
this?

And the secondary question is, if not then is there a standard macro
name and syntax I should use, like the standard "#define
STREQ(s,t)(strcmp(s,t) == 0)"?

-- 

      //  Alan J Rosenthal
     //
 \\ //        flaps@csri.toronto.edu, {seismo!utai or utzoo}!utcsri!flaps,
  \//              flaps@toronto on csnet, flaps at utorgpu on bitnet.


"To be whole is to be part; true voyage is return."