PLEASE HELP - odd string sorting related problem

C

cpptutor2000

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
for your help.
 
D

Default User

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
for your help.


Devise and algorithm for comparing such strings.

Implement the algorithm.




Brian
 
P

pete

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
for your help.

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;
}
}
 
K

Keith Thompson

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's obvious about that?
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.
 
C

CBFalconer

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 for your help.

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.
 
G

Gordon Burditt

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.
 
J

J. J. Farrell

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.
 
C

cpptutor2000

It might help if you STATE A PROBLEM.


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).


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.
 
K

Keith Thompson

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
us what your goal is.
 
S

santosh

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
additional context.

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.
 
J

J. J. Farrell

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
routine to implement your algorithm.
 
K

Keith Thompson

CBFalconer said:
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.)
 
C

CBFalconer

Keith said:
.... 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. :)
 

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