Discussion in 'C Programming' started by cpptutor2000@yahoo.com, Oct 19, 2007.

1. ### Guest

Could some C guru provide some hints on my problem? I am trying to
sort an array of character strings, where each string contains
lowercase, uppercase, digits as well as non-alphanumeric characters as
'-', '(' or '/'. Obviously, standard C functions as 'strcmp' would
fail in these cases. I can convert all the non-digit characters to
lowercase, but how do I deal with the non-alphanumeric characters?

, Oct 19, 2007

2. ### Default UserGuest

wrote:

> Could some C guru provide some hints on my problem? I am trying to
> sort an array of character strings, where each string contains
> lowercase, uppercase, digits as well as non-alphanumeric characters as
> '-', '(' or '/'. Obviously, standard C functions as 'strcmp' would
> fail in these cases. I can convert all the non-digit characters to
> lowercase, but how do I deal with the non-alphanumeric characters?
> Any hints or suggestions would be greatly helpful. Thanks in advance

Devise and algorithm for comparing such strings.

Implement the algorithm.

Brian

Default User, Oct 20, 2007

3. ### peteGuest

wrote:
>
> Could some C guru provide some hints on my problem? I am trying to
> sort an array of character strings, where each string contains
> lowercase, uppercase, digits as well as non-alphanumeric characters as
> '-', '(' or '/'. Obviously, standard C functions as 'strcmp' would
> fail in these cases. I can convert all the non-digit characters to
> lowercase, but how do I deal with the non-alphanumeric characters?
> Any hints or suggestions would be greatly helpful. Thanks in advance

You could use a case insensitive variation on strcmp:

#include <ctype.h>
int str_ccmp(const char *s1, const char *s2)
{
for (; {
if (*s1 != *s2) {
const int c1 = tolower((unsigned char)*s1);
const int c2 = tolower((unsigned char)*s2);

if (c2 != c1) {
return c2 > c1 ? -1 : 1;
}
} else {
if (*s1 == '\0') {
return 0;
}
}
++s1;
++s2;
}
}

--
pete

pete, Oct 20, 2007
4. ### Keith ThompsonGuest

"" <> writes:
> Could some C guru provide some hints on my problem? I am trying to
> sort an array of character strings, where each string contains
> lowercase, uppercase, digits as well as non-alphanumeric characters as
> '-', '(' or '/'. Obviously, standard C functions as 'strcmp' would
> fail in these cases.

> I can convert all the non-digit characters to
> lowercase, but how do I deal with the non-alphanumeric characters?

I don't know. How do you want to deal with non-alphanumeric characters?

Using strcmp() directly is certainly a valid way to sort strings, but
you apparently want to map uppercase letters to lowercase before
comparing them. That still leaves a plethora of ways you might want
to compare strings that contain things other than letters. We have no
way of knowing (and C doesn't define) which of those ways is valid.

You need to decide how you want to do the comparisons. Once you've
done that, it's likely you'll be able to implement the comparison in C
yourself. If not, show us what you've tried and we can help you fix
it.

--
Keith Thompson (The_Other_Keith) <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

Keith Thompson, Oct 20, 2007
5. ### CBFalconerGuest

"" wrote:
>
> Could some C guru provide some hints on my problem? I am trying
> to sort an array of character strings, where each string contains
> lowercase, uppercase, digits as well as non-alphanumeric
> characters as '-', '(' or '/'. Obviously, standard C functions as
> 'strcmp' would fail in these cases. I can convert all the
> non-digit characters to lowercase, but how do I deal with the
> non-alphanumeric characters? Any hints or suggestions would be

Simply apply strcmp. The strings will be sorted in accordance with
the native ordering of the default char set. The sort will
succeed. Whether it is what you want is another matter, and you
can make whatever substitutions you need to affect that.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>

--
Posted via a free Usenet account from http://www.teranews.com

CBFalconer, Oct 20, 2007
6. ### Gordon BurdittGuest

>Could some C guru provide some hints on my problem? I am trying to

It might help if you STATE A PROBLEM.

>sort an array of character strings, where each string contains
>lowercase, uppercase, digits as well as non-alphanumeric characters as
>'-', '(' or '/'. Obviously, standard C functions as 'strcmp' would
>fail in these cases.

It is obvious to me that strcmp() would succeed in comparing any C
strings whatever, as long as you put no requirements on sort order
that conflict with what strcmp() does (and you didn't say anything

>I can convert all the non-digit characters to
>lowercase, but how do I deal with the non-alphanumeric characters?

It isn't necessary to convert punctuation to lower case in any
character set I'm aware of.

It is generally considered a hanging offense to deal characters
from the bottom of the deck.

Gordon Burditt, Oct 20, 2007
7. ### J. J. FarrellGuest

On Oct 19, 11:57 pm, "" <>
wrote:
> Could some C guru provide some hints on my problem? I am trying to
> sort an array of character strings, where each string contains
> lowercase, uppercase, digits as well as non-alphanumeric characters as
> '-', '(' or '/'. Obviously, standard C functions as 'strcmp' would
> fail in these cases.

What do you mean by "fail"? strcmp() will work perfectly well in these
cases.

> I can convert all the non-digit characters to
> lowercase, but how do I deal with the non-alphanumeric characters?

I've no idea - it depends how you want to deal with them. Why do you
want to do anything other than use their normal values?

> Any hints or suggestions would be greatly helpful.

You need to define exactly what you want to do, then write code to do
it.

J. J. Farrell, Oct 20, 2007
8. ### Guest

On Oct 19, 8:28 pm, (Gordon Burditt) wrote:
> >Could some C guru provide some hints on my problem? I am trying to

>
> It might help if you STATE A PROBLEM.
>
> >sort an array of character strings, where each string contains
> >lowercase, uppercase, digits as well as non-alphanumeric characters as
> >'-', '(' or '/'. Obviously, standard C functions as 'strcmp' would
> >fail in these cases.

>
> It is obvious to me that strcmp() would succeed in comparing any C
> strings whatever, as long as you put no requirements on sort order
> that conflict with what strcmp() does (and you didn't say anything
> about sort order at all).
>
> >I can convert all the non-digit characters to
> >lowercase, but how do I deal with the non-alphanumeric characters?

>
> It isn't necessary to convert punctuation to lower case in any
> character set I'm aware of.
>
> It is generally considered a hanging offense to deal characters
> from the bottom of the deck.

As far as I remember from my trusty K & R C text,
the source code for the strcmp fumction is:

int strcmp(const char *s1, const char *s2)
{
while (*s1 == *s2++)
if (*s1++ == 0)
return (0);
return (*(const unsigned char *)s1 - *(const unsigned char *)
(s2 - 1));
}

Given that, I am trying to find a way of sorting strings for example:
1. Bungie.net - TCP623
2. Doom(Id Sofware) - version 1
Obviously, the non-digit and non-alphanumeric (a -> z, A - > Z) cannot
be converted to lower case, how do I deal with these special
characters - straightforward application of 'strcmp' would not provide
very accurate results.

, Oct 20, 2007
9. ### Keith ThompsonGuest

"" <> writes:
[...]
> As far as I remember from my trusty K & R C text,
> the source code for the strcmp fumction is:
>
> int strcmp(const char *s1, const char *s2)
> {
> while (*s1 == *s2++)
> if (*s1++ == 0)
> return (0);
> return (*(const unsigned char *)s1 - *(const unsigned char *)
> (s2 - 1));
> }

That's one possible definition for strcmp() (I'll assume it's correct,
but I haven't taken the time to check it). But strcmp() is specified
in terms of how it behaves. It needn't even be implemented in C.

> Given that, I am trying to find a way of sorting strings for example:
> 1. Bungie.net - TCP623
> 2. Doom(Id Sofware) - version 1
> Obviously, the non-digit and non-alphanumeric (a -> z, A - > Z) cannot
> be converted to lower case, how do I deal with these special
> characters - straightforward application of 'strcmp' would not provide
> very accurate results.

What. Are. You. Trying. To. Do. ???.

What do you mean by "accurate"?

There is no one definition of how to compare strings. You've told us
that you want to treat corresponding upper and lower case letters as
if they were equal ('A' and 'a' equal). You haven't given us a clue
about how you want to deal with non-alphanumeric characters.

For example, if you're comparing "foobar" vs. "FooBarBaz", you
apparently want to map all letters to lowercase, then use strcmp() to
compare "foobar" vs. "foobarbaz" (result: "foobar" < "FooBarBaz").

What if you're comparing "foo.bar" vs. "foo:bar"? What result do you
want? Do you want them to compare equal? Do you want "foo.bar" <
"foo:bar"? or "foo.bar" > "foo:bar"? Or do you not care as long as
you get a consistent ordering? Any of those would be equally correct.

We can't possibly guess how to accomplish your goal if you won't tell

--
Keith Thompson (The_Other_Keith) <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

Keith Thompson, Oct 20, 2007
10. ### santoshGuest

wrote:

> On Oct 19, 8:28 pm, (Gordon Burditt) wrote:
>> >Could some C guru provide some hints on my problem? I am trying to

>>
>> It might help if you STATE A PROBLEM.
>>
>> >sort an array of character strings, where each string contains
>> >lowercase, uppercase, digits as well as non-alphanumeric characters
>> >as '-', '(' or '/'. Obviously, standard C functions as 'strcmp'
>> >would fail in these cases.

>>
>> It is obvious to me that strcmp() would succeed in comparing any C
>> strings whatever, as long as you put no requirements on sort order
>> that conflict with what strcmp() does (and you didn't say anything
>> about sort order at all).
>>
>> >I can convert all the non-digit characters to
>> >lowercase, but how do I deal with the non-alphanumeric characters?

>>
>> It isn't necessary to convert punctuation to lower case in any
>> character set I'm aware of.
>>
>> It is generally considered a hanging offense to deal characters
>> from the bottom of the deck.

>
> As far as I remember from my trusty K & R C text,
> the source code for the strcmp fumction is:
>
> int strcmp(const char *s1, const char *s2)
> {
> while (*s1 == *s2++)
> if (*s1++ == 0)
> return (0);
> return (*(const unsigned char *)s1 - *(const unsigned char
> *)
> (s2 - 1));
> }
>
> Given that, I am trying to find a way of sorting strings for example:
> 1. Bungie.net - TCP623
> 2. Doom(Id Sofware) - version 1
> Obviously, the non-digit and non-alphanumeric (a -> z, A - > Z) cannot
> be converted to lower case, how do I deal with these special
> characters - straightforward application of 'strcmp' would not provide
> very accurate results.

Sorting only makes sense when the data are related or are given
meaningful relatedness by the programmer. Your two strings are only
very tenuously related without _you_ as the programmer giving

IOW, you'll have to define a set of rules on how to sort your data and
write your own sorting function. Of course it can itself use strcmp and
co., at a lower level for parts of the data.

santosh, Oct 20, 2007
11. ### J. J. FarrellGuest

On Oct 20, 9:01 pm, "" <>
wrote:
> On Oct 19, 8:28 pm, (Gordon Burditt) wrote:
>
>
>
>
>
> > >Could some C guru provide some hints on my problem? I am trying to

>
> > It might help if you STATE A PROBLEM.

>
> > >sort an array of character strings, where each string contains
> > >lowercase, uppercase, digits as well as non-alphanumeric characters as
> > >'-', '(' or '/'. Obviously, standard C functions as 'strcmp' would
> > >fail in these cases.

>
> > It is obvious to me that strcmp() would succeed in comparing any C
> > strings whatever, as long as you put no requirements on sort order
> > that conflict with what strcmp() does (and you didn't say anything
> > about sort order at all).

>
> > >I can convert all the non-digit characters to
> > >lowercase, but how do I deal with the non-alphanumeric characters?

>
> > It isn't necessary to convert punctuation to lower case in any
> > character set I'm aware of.

>
> > It is generally considered a hanging offense to deal characters
> > from the bottom of the deck.

>
> As far as I remember from my trusty K & R C text,
> the source code for the strcmp fumction is:
>
> int strcmp(const char *s1, const char *s2)
> {
> while (*s1 == *s2++)
> if (*s1++ == 0)
> return (0);
> return (*(const unsigned char *)s1 - *(const unsigned char *)
> (s2 - 1));
> }
>
> Given that,

I've no idea if that's how K&R implement it, or if what you give above
implements strcmp. I'll assume we're talking about the strcmp that's
part of C.

> I am trying to find a way of sorting strings for example:
> 1. Bungie.net - TCP623
> 2. Doom(Id Sofware) - version 1
> Obviously, the non-digit and non-alphanumeric (a -> z, A - > Z) cannot
> be converted to lower case,

Why not? If it's appropriate to do such a conversion for whatever
comparison algorithm you're trying to implement, it's obvious that
they can.

> how do I deal with these special
> characters

However you want!

> - straightforward application of 'strcmp' would not provide
> very accurate results.

It would provide entirely accurate results. If the results it provides
aren't the results you want, you need to define exactly how you want
the different characters to compare and then write a comparison

J. J. Farrell, Oct 21, 2007
12. ### Keith ThompsonGuest

CBFalconer <> writes:
> "" wrote:
>> Could some C guru provide some hints on my problem? I am trying
>> to sort an array of character strings, where each string contains
>> lowercase, uppercase, digits as well as non-alphanumeric
>> characters as '-', '(' or '/'. Obviously, standard C functions as
>> 'strcmp' would fail in these cases. I can convert all the
>> non-digit characters to lowercase, but how do I deal with the
>> non-alphanumeric characters? Any hints or suggestions would be

>
> Simply apply strcmp. The strings will be sorted in accordance with
> the native ordering of the default char set. The sort will
> succeed. Whether it is what you want is another matter, and you
> can make whatever substitutions you need to affect that.

The OP has already made it clear that the ordering provided by
strcmp() will not meet his requirements, since he wants to map
uppercase letters to lowercase. Unfortunately, that's *all* he's made
clear.

(Strictly speaking, nothing in the C standard prohibits a character
set with an ordering like 'A', 'a', 'B', 'b', 'C', 'c', ..., but I
know of no actual character set that does this.)

--
Keith Thompson (The_Other_Keith) <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

Keith Thompson, Oct 22, 2007
13. ### CBFalconerGuest

Keith Thompson wrote:
>

.... snip ...
>
> (Strictly speaking, nothing in the C standard prohibits a character
> set with an ordering like 'A', 'a', 'B', 'b', 'C', 'c', ..., but I
> know of no actual character set that does this.)

I did that for a cross-reference program 20 years ago. It involved
two 256 byte conversion tables. One was applied at input, and the
other on eventual output. Debugging was a bear until I stopped
using shortcuts.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net>

--
Posted via a free Usenet account from http://www.teranews.com

CBFalconer, Oct 23, 2007