Re: parse two field file
- From: Dave Thompson <david.thompson1@xxxxxxxxxxxxxxxx>
- Date: Wed, 03 Jan 2007 19:42:00 GMT
On Sun, 17 Dec 2006 10:37:28 -0500, Eric Sosman
<esosman@xxxxxxxxxxxxxxxxxxx> wrote:
Richard wrote:
Which way would you guys recommened to best parse a multiline file which containsstrtok(..., "\t") will [lose empty fields]
two fields seperated by a tab. <snip>
Right.
fgets() plus sscanf() is a possibility, but it's a bit
tricky to use: The obvious "%s\t%s" will not do what you
want. (The first "%s" will skip any leading white space,
leaving you in the same hole as the strtok() approach, and
the "\t" will match any amount of any kind of white space,
tabs or other.) Something like "%[^\t]%*1[\t]%s" would do
a little better, but still wouldn't be fully satisfactory:
Not enough better. If the first field is empty and thus the first
%[^\t] matches nothing, *scanf stops and doesn't do the %*1[\t]s.
This is effectively the same problem of the people who periodically
try to use {,f}scanf to replace <ILLEGAL> fflush (input) </>.
(Some people, including IIRC Dan Pop, have recommended e.g.
if( scanf ("%*[^\n]%*1[\n]") < 2 ) getchar ();
but I consider that too much uglier than the obvious, though slightly
longer and possibly slightly less efficient
while( (ch = getchar()) != EOF && ch != '\n' ) ;
etc.
Plus unbounded %[...] or %s risks buffer overflow and resulting UB.
You should specify a length at most one less than the buffer size.
It would match the prefix of "foo\tbar baz goozle frobnitz"
without any warning of the trailing junk. You could use
"%[^\t]%*1[\t]%s%n" and then check that sscanf() had in fact
consumed the entire string ...
... but wouldn't it be simpler just to pick the line
apart for yourself? Read it in with fgets(), use strchr()
to find the first tab <snip>
Yes.
The "most efficient manor" is the house of Usher. ResistYes. Or even the hundred-year shay, IIRC grade school. <G>
this unnecessary impulse for efficiency, lest your program meet
the same fate as did that storied manse.
- David.Thompson1 at worldnet.att.net
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