Sorting Array of Structures

[Allie]

How would I go about sorting this structure by title?

typedef struct {
char author[40];
char title[40];
char code[4];
int hold;
int loan;
} LIBRARY;

LIBRARY book[N];


This is what I've written:

void sortbytitle( LIBRARY *b, int n ) { /* n = number of books in stock
*/
LIBRARY temp[N];
int i;

for( i = 0; i < n; i++ ) {
if( strcmp( b.title, b[i + 1].title ) > 0 ) {
temp = b;
b = b[i + 1];
b[i + 1] = temp;
}
}

return;
}

I get no errors or warnings when I compile using Bloodshed Dev-C++.
However, my output then looks like this:
AUTHOR TITLE CODE #COPY #BORR #AVAIL
Golumbic Graph Theory G01 5 2 3
Jacobs Database Logic J01 3 1 2
Kanter Management Information K01 8 1 7
Kuo Numerical Methods K02 2 0 2
Habermann Operating Systems H01 10 5 5
Schroder C S01 7 2 5
Herzog Computing Structures H03 10 7 3
Holub Compiler Design H05 11 8 3
Galvin Operating Systems G02 15 2 13
Lane Data Communications L01 20 3 17
Kleinrock Queueing Systems K03 14 0 14
Kindred Data Systems K04 2 0 2
Horowitz Programming Languages H06 16 10 6

(Original output, before sort is called:
AUTHOR TITLE CODE #COPY #BORR #AVAIL
Habermann Operating Systems H01 10 5 5
Golumbic Graph Theory G01 5 2 3
Jacobs Database Logic J01 3 1 2
Kanter Management Information K01 8 1 7
Kuo Numerical Methods K02 2 0 2
Hughs Structured Programming H02 4 4 0
Schroder C S01 7 2 5
Herzog Computing Structures H03 10 7 3
Hunter Understanding C H04 6 6 0
Holub Compiler Design H05 11 8 3
Galvin Operating Systems G02 15 2 13
Lane Data Communications L01 20 3 17
Kleinrock Queueing Systems K03 14 0 14
Kindred Data Systems K04 2 0 2
Mano Computer Architecture M01 2 2 0
Horowitz Programming Languages H06 16 10 6

The sortbytitle() function is used in conjunction with
printbyavail()... which explains the three missing books in the output
produced by sortybytitle().)

The titles aren't sorted properly! What am I doing wrong?

Thank you muchly

--Allie

 

[Vladimir S. Oka]

How would I go about sorting this structure by title?

typedef struct {
char author[40];
char title[40];
char code[4];
int hold;
int loan;
} LIBRARY;

LIBRARY book[N];

It may be easiest to use `qsort` function. Look it up.

--
BR, Vladimir

Man is a military animal,
Glories in gunpowder, and loves parade.
-- P.J. Bailey

 

[Richard Heathfield]

Allie said:

How would I go about sorting this structure by title?

typedef struct {
char author[40];
char title[40];
char code[4];
int hold;
int loan;
} LIBRARY;

LIBRARY book[N];

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

int complib(const void *vp1, const void *vp2)
{
const LIBRARY *p1 = vp1;
const LIBRARY *p2 = vp2;
return strcmp(p1->title, p2->title);
}

int main(void)
{
getyourdataintothearray();

qsort(book, sizeof book / sizeof book[0], sizeof book[0], complib);

printyourdata();

return 0;
}

 

[Allie]

Thanks for your response!

I get this as output now:

AUTHOR TITLE CODE #COPY #BORR #AVAIL
Schroder C S01 7 2 5
Holub Compiler Design H05 11 8 3
Herzog Computing Structures H03 10 7 3
Lane Data Communications L01 20 3 17
Kindred Data Systems K04 2 0 2
Jacobs Database Logic J01 3 1 2

It's missing 8 books

--Allie

 

[Allie]

It's missing 8 books

....Or seven, rather.

 

[Alesak]

That looks to me like a really naive code.

1.) the cycle will reach behind the buffer in it's last leap

2.) the algorithm seems to me like a one half of bubblesort, but I
cannot imagine, why you have your "temp" as a buffer, the other thing
is that assigning structure variable to other structure variable does a
blasphemous plenty of memory copying (and I do believe that true C-man
avoids that). The right way to sort array of structures is to sort an
array of pointers. And much, much better than (even not spoilt)
bubblesort is to use library func, like that:

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

typedef struct {
char author[40];
char title[40];
char code[4];
int hold;
int loan;

} LIBRARY;

static int cmplib (const void *a, const void *b)
{
return (strcmp (((LIBRARY*)a)->title, ((LIBRARY*)b)->title));
}
void do_sort (LIBRARY **l, int count)
{
qsort (l, count, sizeof (LIBRARY*), cmplib);
}

 

[Allie]

To Richard: qsort( book, n, sizeof( book[0] ), comptitle ); gives me
the right output. You had written qsort( book, sizeof( book ) / sizeof
(book[0] ), sizeof book[0], comptitle ); Thanks for your help!

To Alesak: I'm not a very seasoned programmer. In fact, I'm just a
student still learning the C language. The last time I touched C was
nine months ago... so I'm a little rusty. But I appreciate any and all
help I get (because sometimes I don't know what I'm doing wrong so that
I can't look up the solution to my problem). So thank you

 

[Flash Gordon]

How would I go about sorting this structure by title?

Unless you have specific reason not to I would suggest looking up qsort
in your C text book.

typedef struct {
char author[40];
char title[40];
char code[4];
int hold;
int loan;
} LIBRARY;

LIBRARY book[N];


This is what I've written:

void sortbytitle( LIBRARY *b, int n ) { /* n = number of books in stock
*/
LIBRARY temp[N];

Why make this an array? You only use each element once.
LIBRARY temp;

int i;

for( i = 0; i < n; i++ ) {

You are doing one too many elements. There is no element after the last
element for you to compare against and possibly swap with!
for( i = 0; i < n-1; i++ ) {

if( strcmp( b.title, b[i + 1].title ) > 0 ) {
temp = b;

temp = b;

b = b[i + 1];
b[i + 1] = temp;

b[i+1] = temp;

}
}

return;
}

I get no errors or warnings when I compile using Bloodshed Dev-C++.

<snip>

Not surprising, your only C error is going off the end of your array,
and compilers don't have to complain about that.

You also have a major algorithm error, but we only do C here not
algorithms. I believe comp.programming does algorithms, so if you need
to implement a sort algorithm (I'm guessing that is your assignment and
your reason for not using qsort) then that is the place to ask.

However, here are some hint for you:

How can you move an element from position 2 to position 0? Your
implementation can at most move it to position 1.

Google for "bubble sort" since I think that is what you are trying to
implement and it is also nice and easy to understand. There are more
efficient algorithms, but they are harder to understand and you should
start with the simplest approach.

 

[Default User]

Thanks for your response!

I get this as output now:

How can we fix code we can't see? Post a complete, minimal program,
plus the data.

Also, read the information below.


Brian

 

[Keith Thompson]

To Richard: qsort( book, n, sizeof( book[0] ), comptitle ); gives me
the right output. You had written qsort( book, sizeof( book ) / sizeof
(book[0] ), sizeof book[0], comptitle ); Thanks for your help!

Richard's sizeof(book) / sizeof(book[0] assumes you want to sort the
entire array; apparently you just want to sort the first n entries.

 

[Keith Thompson]

Google for "bubble sort" since I think that is what you are trying to
implement and it is also nice and easy to understand. There are more
efficient algorithms, but they are harder to understand and you should
start with the simplest approach.

Bubble sort is a decent good starting point if you're trying to
understand the process of sorting; it's fairly simple, and it's
relatively easy to understand how it works. But it also happens to be
one of the *least* efficient sorting algorithms, at least among those
that weren't deliberately designed for inefficiency. [*]

But the simplest way to sort something in C is to use the predefined
qsort() function. It has the advantage that the algorithm itself is
likely to be as efficient as possible, or nearly so. The
disadvantages are that the interface imposes some overhead (an
indirect function call for each comparison), and you can't necessarily
see the algorithm (which isn't necessarily Quicksort).

[*]
One of my favorite "pessimal" sorting algorithms is Permutation
Sort. Starting with an array of elements, generate all possible
permutations. Check each permutation to see whether it happens to be
sorted. (An optimized version allows you to stop at this point;
otherwise you can save the sorted permutation and continue to generate
all the others.)

Another really bad technique is Miracle Sort (which, strictly
speaking, doesn't qualify as an algorithm). Start with an array of
elements. Check whether it's sorted. If it is, you're done.
Otherwise, wait a while and check again. Pray for cosmic rays or
other fortuitous memory faults.

 

[Jordan Abel]

To Richard: qsort( book, n, sizeof( book[0] ), comptitle ); gives me
the right output. You had written qsort( book, sizeof( book ) / sizeof
(book[0] ), sizeof book[0], comptitle ); Thanks for your help!

Richard's sizeof(book) / sizeof(book[0] assumes you want to sort the
entire array; apparently you just want to sort the first n entries.

or "book" is a pointer and "n" is the number of entries in the array it
points at the first element of.

 

[Ben Pfaff]

Another really bad technique is Miracle Sort (which, strictly
speaking, doesn't qualify as an algorithm). Start with an array of
elements. Check whether it's sorted. If it is, you're done.
Otherwise, wait a while and check again. Pray for cosmic rays or
other fortuitous memory faults.

My guess is that it's more likely for the processor to
malfunction and decide that the data is sorted, when it really is
not,than it is for the malfunction to change the data to sorted
order.

 

[Keith Thompson]

To Richard: qsort( book, n, sizeof( book[0] ), comptitle ); gives me
the right output. You had written qsort( book, sizeof( book ) / sizeof
(book[0] ), sizeof book[0], comptitle ); Thanks for your help!

Richard's sizeof(book) / sizeof(book[0] assumes you want to sort the
entire array; apparently you just want to sort the first n entries.

or "book" is a pointer and "n" is the number of entries in the array it
points at the first element of.

In the original code (since snipped), "book" was an array.

 

[Keith Thompson]

My guess is that it's more likely for the processor to
malfunction and decide that the data is sorted, when it really is
not,than it is for the malfunction to change the data to sorted
order.

Not if the technique lives up to its name.

(Amusing typo: I initially left the 'v' out of "lives".)

 

[Flash Gordon]

Google for "bubble sort" since I think that is what you are trying to
implement and it is also nice and easy to understand. There are more
efficient algorithms, but they are harder to understand and you should
start with the simplest approach.

Bubble sort is a decent good starting point if you're trying to
understand the process of sorting; it's fairly simple, and it's
relatively easy to understand how it works. But it also happens to be
one of the *least* efficient sorting algorithms, at least among those
that weren't deliberately designed for inefficiency. [*]

But the simplest way to sort something in C is to use the predefined
qsort() function. It has the advantage that the algorithm itself is

<snip>

Yes, I know. I even said in the text you snipped, "Unless you have
specific reason not to I would suggest looking up qsort in your C text
book." I went on to say, still before the bit you snipped, "... so if
you need to implement a sort algorithm (I'm guessing that is your
assignment and your reason for not using qsort) ..."

Personally I have never bothered implementing a sort algorithm myself
and probably never will. If I need something better than qsort I'll ask
experts and then use an implementation written by someone else.

 

[Keith Thompson]

Google for "bubble sort" since I think that is what you are trying to
implement and it is also nice and easy to understand. There are more
efficient algorithms, but they are harder to understand and you should
start with the simplest approach.

Bubble sort is a decent good starting point if you're trying to
understand the process of sorting; it's fairly simple, and it's
relatively easy to understand how it works. But it also happens to be
one of the *least* efficient sorting algorithms, at least among those
that weren't deliberately designed for inefficiency. [*]
But the simplest way to sort something in C is to use the predefined
qsort() function. It has the advantage that the algorithm itself is

<snip>

Yes, I know. I even said in the text you snipped, "Unless you have
specific reason not to I would suggest looking up qsort in your C text
book." I went on to say, still before the bit you snipped, "... so if
you need to implement a sort algorithm (I'm guessing that is your
assignment and your reason for not using qsort) ..."

So you did. My apologies for not reading carefully enough.

 

[CBFalconer]

My guess is that it's more likely for the processor to
malfunction and decide that the data is sorted, when it really is
not,than it is for the malfunction to change the data to sorted
order.

Another possibility is operator malfunction, making the other
malfunctions more or less moot. Many of us are already pushing our
MTBF values.

--
"If you want to post a followup via groups.google.com, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson
More details at: <http://cfaj.freeshell.org/google/>
Also see <http://www.safalra.com/special/googlegroupsreply/>

 

[Richard Heathfield]

Allie said:

To Richard: qsort( book, n, sizeof( book[0] ), comptitle ); gives me
the right output. You had written qsort( book, sizeof( book ) / sizeof
(book[0] ), sizeof book[0], comptitle );

What I wrote was based on the information you gave me. If you gave me the
wrong information, that is your lookout, not mine.

Incidentally, you have misquoted me. I most certainly did not write:

sizeof( book ) / sizeof (book[0] )

If you wish to become a successful programmer, you will need to develop a
more pedantic approach with regard to accuracy, precision, and correctness.

 

[James Dow Allen]

Many of us are already pushing our MTBF values.

Gather ye rosebuds while ye may.