martin@mwtech.UUCP (Martin Weitzel) (11/15/90)
In article <VXogs2w163w@cybrspc> roy%cybrspc@cs.umn.edu (Roy M. Silvernail) writes: >[about reading formatted input] It's better, IMHO, to gets() a whole >line, check its validity and _then_ sscanf() it into the target >variables. (no need for strtol() or similar, since sscanf() looks at the >validated string just as scanf() would have looked at the original >input) It just makes things more bullet-resistant. I agree completly, except for one point: Bullet resistant programs should never use gets() -- fgets() is the way to go! BTW: Recently there occured a problem, to which I couldn't find an immediate solution. Take the following program fragment: #define X 100 char word[X+1]; int z; scanf("%100[^:]:%d", word, &z); ^^^----------------------- I'd rather want X here; still better were `(sizeof word) - 1', so that I could ommit the #define for X completly What I want is to have only *one* place where I define the length of a word. In this example, if I change the #define of X, I must never forget to make a change at a second place, which may be far away from the first. What I could do is dynamically (at runtime) construct an appropriate format specification. But IMHO this more a work-around than an elegant solution to the problem. -- Martin Weitzel, email: martin@mwtech.UUCP, voice: 49-(0)6151-6 56 83
fisher@sc2a.unige.ch (11/16/90)
In article <960@mwtech.UUCP>, martin@mwtech.UUCP (Martin Weitzel) writes: > [...] > BTW: Recently there occured a problem, to which I couldn't find an > immediate solution. Take the following program fragment: > > #define X 100 > char word[X+1]; int z; > > scanf("%100[^:]:%d", word, &z); > ^^^----------------------- I'd rather want X here; still > better were `(sizeof word) - 1', so that I could ommit > the #define for X completly Yeah, it would be nice if we could have a `scanf("%*s", sizeof(word), word)' printf-like type of construct, but then the `*' is already used for something else... As another workaround, it seems that some compilers *do* expand macros inside strings and character constants, in which case you could use the `X' there. If not, try to look in the the `Token Replacement' chapter of your compiler's `User Guide'. In TC, for example, you can "stringize" a macro, with the `#' symbol (i.e. `#X' is converted to `"100"'). Another feature of TC is the automatic concatenation of string literals (i.e. `"hello " "world"' becomes `"hello world"'). With these features, you can rewrite your example as scanf("%" #X "[^:]:%d", word, &z); Not really portable, you this can be useful. Markus Fischer, Dpt of Anthropology, Geneva.
scjones@thor.UUCP (Larry Jones) (11/17/90)
In article <960@mwtech.UUCP>, martin@mwtech.UUCP (Martin Weitzel) writes: > BTW: Recently there occured a problem, to which I couldn't find an > immediate solution. Take the following program fragment: > > #define X 100 > char word[X+1]; int z; > > scanf("%100[^:]:%d", word, &z); > ^^^----------------------- I'd rather want X here; still > better were `(sizeof word) - 1', so that I could ommit > the #define for X completly > > What I could do is dynamically (at runtime) construct an appropriate > format specification. But IMHO this more a work-around than an elegant > solution to the problem. Yes. I never did understand why printf allowed "*" for run-time specification of field width and precision, but scanf usurped "*" for assignment suppression and so doesn't support run-time field widths. Any historians know how this came to be? ---- Larry Jones UUCP: uunet!sdrc!thor!scjones SDRC scjones@thor.UUCP 2000 Eastman Dr. BIX: ltl Milford, OH 45150-2789 AT&T: (513) 576-2070 Physical education is what you learn from having your face in someone's armpit right before lunch. -- Calvin
karl@ima.isc.com (Karl Heuer) (11/18/90)
In article <1990Nov16.125504.305@sc2a.unige.ch> fisher@sc2a.unige.ch writes: >As another workaround, it seems that some compilers *do* expand macros inside >strings and character constants, in which case you could use the `X' there. I refuse to believe that. Some non-ANSI preprocessors expand *macro arguments* inside string literals within the macro, but I've never heard of one that expanded macros in string literals in the program. It would break too much code. >In TC, for example, you can "stringize" a macro... It's not a TC invention; stringizing and string literal pasting are available in all ANSI C compilers. Note that it doesn't help you if X was defined as an expression like `(99+1)', since the C preprocessor (unlike, say, m4) doesn't have a way to reduce constant expressions. Karl W. Z. Heuer (karl@ima.isc.com or uunet!ima!karl), The Walking Lint
avery@netcom.UUCP (Avery Colter) (11/22/90)
martin@mwtech.UUCP (Martin Weitzel) writes: > scanf("%100[^:]:%d", word, &z); > ^^^----------------------- I'd rather want X here; still > better were `(sizeof word) - 1', so that I could ommit > the #define for X completly >What I could do is dynamically (at runtime) construct an appropriate >format specification. But IMHO this more a work-around than an elegant >solution to the problem. It may be the only way unfortunately, unless you have some interesting preprocessor at your disposal. How about just defining a string and an unsigned, uhh, lessee, assign X to the unsigned, then make sscanf(string," %u",&uns.int), and then a couple of strcats to put the rest of the format string around it, and voilla. What is inelegant about this? Or am I dealing with people who think that code has to be a candidate for the SI Swimsuit Issue to be called elegant? -- Avery Ray Colter {apple|claris}!netcom!avery {decwrl|mips|sgi}!btr!elfcat (415) 839-4567 "I feel love has got to come on and I want it: Something big and lovely!" - The B-52s, "Channel Z"
avery@netcom.UUCP (Avery Colter) (11/22/90)
Oh yes...
Another thing in scanf's favor over gets...
While reading the new and improved 10 commandments, I was reminded of
gets' nasty habit of taking any size line given to it.
But I suppose fgets takes care of that... you just have to whack off
the endline character somehow.
--
Avery Ray Colter {apple|claris}!netcom!avery {decwrl|mips|sgi}!btr!elfcat
(415) 839-4567 "I feel love has got to come on and I want it:
Something big and lovely!" - The B-52s, "Channel Z"ok@goanna.cs.rmit.oz.au (Richard A. O'Keefe) (11/23/90)
In article <17295@netcom.UUCP>, avery@netcom.UUCP (Avery Colter) writes: > Another thing in scanf's favor over gets... > While reading the new and improved 10 commandments, I was reminded of > gets' nasty habit of taking any size line given to it. Why is this a point in favour of scanf()? scanf("%[^\n]%*c", buff) >= 0 and gets(buff) != NULL do pretty much the same thing; scanf() will "take any size line given to it". -- I am not now and never have been a member of Mensa. -- Ariadne.