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Re: "stop and wait" scanf [was Re: Bug in TRE regular expression library]
- Subject: Re: "stop and wait" scanf [was Re: Bug in TRE regular expression library]
- From: Ralf Junker <ralfjunker%gmx.de@localhost>
- Date: Wed, 21 Jul 2010 08:54:42 +0200
On 20.07.2010 22:53, der Mouse wrote:
>> I never put any thought into this scanf arguments, simply because
>> > they serve a single purpose: Stop the application so I can read its
>> > output and press any key to quit quickly. Works fine for me here.
> It actually looks as though you meant to write "%*s" but got the * and
> % switched. %*s is not quite what you want either, since it will
> silently consume whitespace, including newlines.
As I thought about it once more and read some docs I recall that
scanf("%*s") is indeed what I intended. Thanks for the clearing this up.
>You might want %*c,
> but that will consume only the next character, rather than up to the
> next newline (which I suspect is what you want) - scanf("%*c") is
> pretty much the same as getchar() in this use.
I tested and found that getchar(), scanf("%*c"), and scanf("%*s") are
working likewise well for my purpose.
> There is actually a syntax that is very close to what I think you want:
> scanf("%*[^\n]"). The * suppresses assignment, so you don't have to
> pass a pointer, and the format spec says to consume a string of
> unlimited length made up of non-newlines. However, it does not consume
> the \n, so if you use it twice, the second call will return
> immediately. It might work to do scanf("%*[^\n]%*1[\n]") (the second
> format specifier attempts to consume at most one newline), but I'd want
> to test that before depending on it - I suspect that's a piece of scanf
> that gets little testing and thus is likely to be buggy.
What I really want is a single command to stop and wait for just _any_
key-press -- not the RETURN key only. Searching the web indicates that
this does not exist, at least not in a simple and platform independent
way. So I can happily live with getchar() as you suggested.
>> > I am sorry to say that I am not much concerned about any problems
>> > this key press might cause elsewehere, as this is not a working
>> > application but some simple code to demonstrate a problem somewhere
>> > else, possibly in production code.
> Normally, I'd feel the same way. But this looks like not a standalone
> test program but a small part of a larger test scaffold, and if running
> one test can corrupt things so as to cause a later test to fail
> spuriously, that sounds to me like a real problem.
I appreciate your concern, but it is in fact just a standalone test program.
Now that this is settled, I would love to read from someone with the
same enthusiasm for my original TRE regular expression problem! ;-)
Below is the test code again, now properly using getchar().
#define p "(.)\\1$"
int _tmain(int argc, _TCHAR* argv)
int nMatches, rc;
TRE_MB_CUR_MAX = 2;
rc = tre_regncomp(&RE, p, strlen(p), REG_EXTENDED);
printf ("%d\n", rc);
nMatches = RE.re_nsub + 1;
matches = malloc (nMatches * sizeof(matches));
rc = tre_regexec(&RE, "foox", nMatches, matches, 0);
printf("Result: %d\n", rc);
getchar(); /* Keep app window open until key press. */
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