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sscanf

If I have
sscanf("FL:%s:%d:%s\n", lGuid, &lID, lFileName);

and the last string contains spaces, e.g. my complete string
"FL:1234ABCD:3:FileName With Spaces.txt\n"

does sscanf just make lFileName the string up to the whitespace? even though
I tell it the end of string as at the \n ?

Thanks
Allan
Nov 14 '05 #1
11 3051

"Allan Bruce" <al*****@TAKEAWAYf2s.com> wrote in message
news:c5**********@news.freedom2surf.net...
If I have
sscanf("FL:%s:%d:%s\n", lGuid, &lID, lFileName);

and the last string contains spaces, e.g. my complete string
"FL:1234ABCD:3:FileName With Spaces.txt\n"

does sscanf just make lFileName the string up to the whitespace? even though I tell it the end of string as at the \n ?

Thanks
Allan


also, is there a way to set ':' as a terminator for the string? I jsut
realised that my lGuid will continue until the next whitespace or \0
Thanks
Allan
Nov 14 '05 #2
"Allan Bruce" <al*****@TAKEAWAYf2s.com> wrote:

"Allan Bruce" <al*****@TAKEAWAYf2s.com> wrote:
If I have
sscanf("FL:%s:%d:%s\n", lGuid, &lID, lFileName); ^
You forgot to specify the string to parse
and the last string contains spaces, e.g. my complete string
"FL:1234ABCD:3:FileName With Spaces.txt\n"

does sscanf just make lFileName the string up to the whitespace? even

though
I tell it the end of string as at the \n ?


also, is there a way to set ':' as a terminator for the string? I jsut
realised that my lGuid will continue until the next whitespace or \0


Warning, untested:

sscanf( yourstring, "FL:%[^:]:%d:%[^\n]\n", lGuid, &lID, lFileName);

If the ':'s might be surrounded by whitespace that should be ignored,
you'll have to match and discard that, too.

HTH
Regards
--
Irrwahn Grausewitz (ir*******@freenet.de)
welcome to clc: http://www.ungerhu.com/jxh/clc.welcome.txt
clc faq-list : http://www.faqs.org/faqs/C-faq/faq/
clc OT guide : http://benpfaff.org/writings/clc/off-topic.html
Nov 14 '05 #3
>
Warning, untested:

sscanf( yourstring, "FL:%[^:]:%d:%[^\n]\n", lGuid, &lID, lFileName);

If the ':'s might be surrounded by whitespace that should be ignored,
you'll have to match and discard that, too.

HTH
Regards


I tried:
sscanf(xiBuffer, "FL:%d:%[^:]s:%d:%[^\n]s\n", &lID, lGUID, &lFileLength,
lFileName);

the lGUID gets read fine, but nothing after this gets read. Where can I
find information about these scan types?
Thanks
Allan
Nov 14 '05 #4
"Allan Bruce" <al*****@TAKEAWAYf2s.com> wrote:

Warning, untested:

sscanf( yourstring, "FL:%[^:]:%d:%[^\n]\n", lGuid, &lID, lFileName);

If the ':'s might be surrounded by whitespace that should be ignored,
you'll have to match and discard that, too.

HTH
Regards
I tried:
sscanf(xiBuffer, "FL:%d:%[^:]s:%d:%[^\n]s\n", [....]

^ ^
You've got two spurious s characters at the indicated positions.
the lGUID gets read fine, but nothing after this gets read. Where can I
find information about these scan types?


Hm, RTFM? ;-)
Seriously, your implementation should provide a documentation of the
standard library functions. Alternatively, buy the C standard, or,
if you're short on money, retrieve a copy of the final public draft
for free at: http://anubis.dkuug.dk/jtc1/sc22/wg14/www/docs/n869/ .
As a starter, here's an excerpt from the *scanf function description:

ISO/IEC 9899:1999
7.19.6.2 The fscanf function
[...]

[ Matches a nonempty sequence of characters from a set of expected
characters (the scanset). If no l length modifier is present, the
corresponding argument shall be a pointer to the initial element of
a character array large enough to accept the sequence and a
terminating null character, which will be added automatically.
[...] The conversion specifier includes all subsequent characters
in the format string, up to and including the matching right
bracket (]). The characters between the brackets (the scanlist)
compose the scanset, unless the character after the left bracket is
a circumflex (^), in which case the scanset contains all characters
that do not appear in the scanlist between the circumflex and the
right bracket. [...]

HTH
Regards
--
Irrwahn Grausewitz (ir*******@freenet.de)
welcome to clc: http://www.ungerhu.com/jxh/clc.welcome.txt
clc faq-list : http://www.faqs.org/faqs/C-faq/faq/
clc OT guide : http://benpfaff.org/writings/clc/off-topic.html
Nov 14 '05 #5
I tried:
sscanf(xiBuffer, "FL:%d:%[^:]s:%d:%[^\n]s\n", [....]

^ ^
You've got two spurious s characters at the indicated positions.
the lGUID gets read fine, but nothing after this gets read. Where can I
find information about these scan types?


Hm, RTFM? ;-)
Seriously, your implementation should provide a documentation of the
standard library functions. Alternatively, buy the C standard, or,
if you're short on money, retrieve a copy of the final public draft
for free at: http://anubis.dkuug.dk/jtc1/sc22/wg14/www/docs/n869/ .


Thanks, I have it working now.
Allan
Nov 14 '05 #6
In <c5**********@news.freedom2surf.net> "Allan Bruce" <al*****@TAKEAWAYf2s.com> writes:
If I have
sscanf("FL:%s:%d:%s\n", lGuid, &lID, lFileName);
You're invoking undefined behaviour, because the input string is missing
from your sscanf call.
and the last string contains spaces, e.g. my complete string
"FL:1234ABCD:3:FileName With Spaces.txt\n"

does sscanf just make lFileName the string up to the whitespace?
Yup.
even though I tell it the end of string as at the \n ?


Nope, you're not telling it anything like that. You're merely telling
it to eat *any* whitespace it finds after the string (which is a noop in
your case, since you're using sscanf and not [f]scanf). There is NO way
to tell %s that the first white space encountered is not ending the input
string. You have to use a more sophisticated conversion descriptor for
this purpose:

#define INPUT "FL:1234ABCD:3:FileName With Spaces.txt\n"

int rc = sscanf(INPUT, "FL:%s:%d:%[^\n]", lGuid, &lID, lFileName);

Things to remember:

1. If lFileName is not large enough to hold the whole first argument of
the sscanf call, use an explicit maximum input field specification; no
need to rediscover the joys of gets. This also applies to %s.

2. Unlike most conversion specifications, including %s, %[ doesn't skip
any preceding white space (just like %c). If needed, use an explicit
white space in the format string, for this purpose (it is harmless if
there is no white space at all at that point in the input string).

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de
Nov 14 '05 #7
In <c5***********@sunnews.cern.ch> I wrote:
In <c5**********@news.freedom2surf.net> "Allan Bruce" <al*****@TAKEAWAYf2s.com> writes:
If I have
sscanf("FL:%s:%d:%s\n", lGuid, &lID, lFileName);


You're invoking undefined behaviour, because the input string is missing
from your sscanf call.
and the last string contains spaces, e.g. my complete string
"FL:1234ABCD:3:FileName With Spaces.txt\n"

does sscanf just make lFileName the string up to the whitespace?


Yup.
even though I tell it the end of string as at the \n ?


Nope, you're not telling it anything like that. You're merely telling
it to eat *any* whitespace it finds after the string (which is a noop in
your case, since you're using sscanf and not [f]scanf). There is NO way
to tell %s that the first white space encountered is not ending the input
string. You have to use a more sophisticated conversion descriptor for
this purpose:

#define INPUT "FL:1234ABCD:3:FileName With Spaces.txt\n"

int rc = sscanf(INPUT, "FL:%s:%d:%[^\n]", lGuid, &lID, lFileName);


Which is plagued by the problem already mentioned downthread by Allan:
%s will eat too much, stopping after FileName. So, %s is not the right
thing for lGuid, either:

int rc = sscanf(INPUT, "FL:%[^:]:%d:%[^\n]", lGuid, &lID, lFileName);

NEVER omit to check rc, to see if all the fields have been properly
converted.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de
Nov 14 '05 #8
If I have
sscanf("FL:%s:%d:%s\n", lGuid, &lID, lFileName);

^

That's a C++ reference operator isn't it? I don't think that has
anything to do with a pointer. It is a COM Interface ID isn't it?

Bill
Nov 14 '05 #9
> the lGUID gets read fine, but nothing after this gets read. Where can I
find information about these scan types?
Thanks
Allan

sscanf reads a string instead of input from a keyboard.
http://www-ccs.ucsd.edu/c/

Bill
Nov 14 '05 #10

"Bill Cunningham" <no****@nspam.net> wrote in message
news:10*************@corp.supernews.com...
If I have
sscanf("FL:%s:%d:%s\n", lGuid, &lID, lFileName);

^

That's a C++ reference operator isn't it? I don't think that has
anything to do with a pointer. It is a COM Interface ID isn't it?

Bill


no, sscanf requires a pointer to write to, this is just an integer declared
the line above as :
int lID;
so the & is taking the address of it to make a pointer on the fly.
Allan
Nov 14 '05 #11
> no, sscanf requires a pointer to write to, this is just an integer
declared
the line above as :
int lID;
so the & is taking the address of it to make a pointer on the fly.
Allan

Oh I see. that IID just looked like an interface identifier.

Bill

Nov 14 '05 #12

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