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sorting arrays...

Posted on 2001-08-08
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Last Modified: 2010-04-02
Hey all, I'm trying to find a quick way to sort an array.  This array has one element, a structure, and this structure has two elements.  Something like this:

struct MyStruct{
   int arg1;
   int arg2;
}MS;

struct MS MyArray[50];

Now I want to sort the array based on arg2.  Does anybody know a quick way of doing this.  I've thought about doing a bubble sort, but there has to be a quicker way.  I've tried using qsort, but I can't figure out how to make it look at arg2 as the sort key.

I need the code in C, not C++, and it must be ANSI compatable and able to run in DOS.  I'm using MS VC 1.52c for MSDOS programs.

Thanks.
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Question by:Ra
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6 Comments
 
LVL 30

Expert Comment

by:Axter
ID: 6365947
FYI,
You might want to post this type of question in the C topic area, or at least post a link to it.
http://www.experts-exchange.com/jsp/qList.jsp?ta=cprog
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LVL 86

Accepted Solution

by:
jkr earned 400 total points
ID: 6365964

>>how to make it look at arg2 as the sort key

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

int compare( const void *arg1, const void *arg2 );

void main( int argc, char **argv )
{

struct MyStruct{
  int arg1;
  int arg2;
}MS;

struct MS MyArray[50];

//....

   qsort( (void *)MyArray, (size_t)50, sizeof( struct MS ), compare );

}

int compare( const void *arg1, const void *arg2 )
{
struct MS* p1 = (struct MS*) arg1;
struct MS* p1 = (struct MS*) arg1;

if ( p1->arg2 > p2->arg2) return ( 1);
if ( p1->arg2 < p2->arg2) return ( -1);
 
 
 return ( 0);
}
0
 

Author Comment

by:Ra
ID: 6366226
Axter, sorry, didn't realize there was a C topic area. ;)

jkr, thanks.  I'll test it when I get to work tomorrow morning.  I never thought about type casting those args to my structure.  It should work great.  I'll give you the points after I test it.
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LVL 86

Expert Comment

by:jkr
ID: 6366505
>>never thought about type casting

In good ol' "C", it's the only way :o)

In C++, using STL would be the idea...
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Author Comment

by:Ra
ID: 6367938
Excellent, it works.  I had to change the second line in the compare function, a little copy and paste error there it looks like. ;)

Thanks jkr.
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LVL 86

Expert Comment

by:jkr
ID: 6367957
>>a little copy and paste error there it looks like. ;)

Yup, I just saw it :o)
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