Sorting a string aray in order of string length

[C.K.]

Given an array of strings (i.e char *strings[10]), write C code to sort the
list in increasing order of string length. Run time efficiency is a primary
concern.

Thanks a lot!

[Tom St Denis]

C.K. wrote:

Given an array of strings (i.e char *strings[10]), write C code to sort the
list in increasing order of string length. Run time efficiency is a primary
concern.

Thanks a lot!

Do your own homework?

Tom

[C.K.]

No, I am now enjoying my summer vacation.

This is a question that I find from 'C Challenge' of a website. I am just
curious on how to solve it in an elegant way.

Thanks in advance!
"Tom St Denis" <to********@iahu.ca> ?????
news:_y********************@news01.bloor.is.net.ca ble.rogers.com...

C.K. wrote:

Given an array of strings (i.e char *strings[10]), write C code to sort the list in increasing order of string length. Run time efficiency is a primary concern.

Thanks a lot!

Do your own homework?

Tom

[pete]

C.K. wrote:

Given an array of strings (i.e char *strings[10]),
write C code to sort the list in increasing order of string length.
Run time efficiency is a primary concern.

#include <string.h>
#include <stdlib.h>

int compare(const void *arg1, const void *arg2)
{
size_t L1, L2;

L1 = strlen(arg1);
L2 = strlen(arg2);
return L2 > L1 ? -1 : L1 > L2;
}

qsort
(strings, sizeof strings/sizeof *strings, sizeof *strings, compare);

[Eric Sosman]

"C.K." wrote:

Given an array of strings (i.e char *strings[10]), write C code to sort the
list in increasing order of string length. Run time efficiency is a primary
concern.

Why is run time efficiency a primary concern when sorting
an array of just ten elements? With such a short array, how
do you even hope to measure the run time to find out what kind
of efficiency you've achieved?

--
Er*********@sun.com

[Chris Dollin]

C.K. wrote:

No, I am now enjoying my summer vacation.

This is a question that I find from 'C Challenge' of a website. I am just
curious on how to solve it in an elegant way.

The best way is to *try it yourself*, *then* ask for suggestions.

--
Chris "electric hedgehog" Dollin
C FAQs at: http://www.faqs.org/faqs/by-newsgrou...mp.lang.c.html
C welcome: http://www.angelfire.com/ms3/bchambl...me_to_clc.html

[Default User]

"C.K." wrote:

No, I am now enjoying my summer vacation.

This is a question that I find from 'C Challenge' of a website. I am just
curious on how to solve it in an elegant way.

Don't top-post. Your replies belong following properly trimmed quotes.

The point of a C challenge is for YOU to work on it. Do your best and
post it here for critique. We don't do programming for random people to
admire.


Brian Rodenborn

[Kevin Easton]

pete <pf*****@mindspring.com> wrote:

C.K. wrote:

Given an array of strings (i.e char *strings[10]),
write C code to sort the list in increasing order of string length.
Run time efficiency is a primary concern.

#include <string.h>
#include <stdlib.h>

int compare(const void *arg1, const void *arg2)
{
size_t L1, L2;

L1 = strlen(arg1);
L2 = strlen(arg2);
return L2 > L1 ? -1 : L1 > L2;
}

qsort
(strings, sizeof strings/sizeof *strings, sizeof *strings, compare);

You obviously didn't test this, because that won't work at all. The
const void * arguments qsort passes to the compare function are pointers
to the array elements - not the array elements themselves. In this
case, they're pointer-to-pointer-to-char, converted to void *. In this
case, the correct comparison function would be:

int lencomp(const void *a, const void *b)
{
char * const *sa = a;
char * const *sb = b;
size_t alen = strlen(*sa);
size_t blen = strlen(*sb);

return (alen > blen) - (alen < blen);
}

- Kevin.

[pete]

Kevin Easton wrote:

pete <pf*****@mindspring.com> wrote:

C.K. wrote:

Given an array of strings (i.e char *strings[10]),
write C code to sort the list in increasing order of string length.
Run time efficiency is a primary concern.

#include <string.h>
#include <stdlib.h>

int compare(const void *arg1, const void *arg2)
{
size_t L1, L2;

L1 = strlen(arg1);
L2 = strlen(arg2);
return L2 > L1 ? -1 : L1 > L2;
}

qsort
(strings, sizeof strings/sizeof *strings, sizeof *strings, compare);

You obviously didn't test this, because that won't work at all.
The const void * arguments qsort passes to the compare function
are pointers to the array elements
- not the array elements themselves.
In this case, they're pointer-to-pointer-to-char,
converted to void *.
In this case, the correct comparison function would be:

int lencomp(const void *a, const void *b)
{
char * const *sa = a;
char * const *sb = b;
size_t alen = strlen(*sa);
size_t blen = strlen(*sb);

return (alen > blen) - (alen < blen);
}

Thank you.
I make a mistake about that bad,
almost every single time that I post untested code.

My compiler likes it better this way:

char const **sa = a;
char const **sb = b;

--
pete

[Kevin Easton]

pete <pf*****@mindspring.com> wrote:

Kevin Easton wrote: [...]

int lencomp(const void *a, const void *b)
{
char * const *sa = a;
char * const *sb = b;

[...] My compiler likes it better this way:

char const **sa = a;
char const **sb = b;

Then your compiler is broken :). const void *a; and char * const *sa;
are equivalently-qualified pointers, but char const **sa; is not. The
first points to a const-qualified void, the second to a const-qualified
pointer to char, but the third points to a non-qualified pointer to a
pointer to const-qualified char.

- Kevin.