Thread: Problem with C functions ?

Hi there,

I compiled a C-funtion to compute the azimuth of a LSEG but the function
never
returns the correct value, but elog( ... ) report the correct value.
So there seems to be a problem returning doubles or floats ??

compile the folling function with
gcc -fPIC -O2 -shared  -o lseg_azimuth.o -c lseg_azimuth.c
-I/opt/local/postgres/include -L/opt/local/postgres/lib
ld -G -Bdynamic -o libgeom.so   lseg_azimuth.o 

#include <math.h>

#include "postgres.h"
#include "utils/geo_decls.h"

double lseg_azimuth( LSEG* lseg );
float add_one( float arg );

double lseg_azimuth( LSEG* lseg )
{ double x1, y1; double x2, y2; double ori;
 x1 = lseg->p[0].x; y1 = lseg->p[0].y;
 x2 = lseg->p[1].x; y2 = lseg->p[1].y;
 ori = atan2( (x2-x1), (y2-y1)); ori = (ori / M_PI) * 200.0;
 if ( ori < 0.0 )   ori += 400.0;
 elog( NOTICE, "ori = %8.3lf", ori );
 return( ori );  
}


then use:

create function lseg_azimuth(lseg) returns float8 as ' ... path to the shared lib you just created ...' language 'c';


create table xxx (geometry lseg);

insert into xxx (geometry) values
('[(4148.675,5414.255),(4151.405,5414.255)]');

select lseg_azimuth(geometry) from xxx;

will return:

NOTICE:  ori =  100.000
lseg_azimuth
------------   4148.675
(1 row)

But that's obviously not what it should be ...

Maybe you have any suggestions ?

many thanks
Manuel
-- 
Manuel Weindorf (weindorf@ipf.bau-verm.uni-karlsruhe.de)
Institut fuer Photogrammetrie und Fernerkundung, Universitaet Karlsruhe
Postfach 6980 D-76128 Karlsruhe Tel. +49721 6086010 Fax +49721 694568
http://www-ipf.bau-verm.uni-karlsruhe.de

On Fri, 12 Nov 1999, Manuel Weindorf wrote:

> Hi there,
> 
> I compiled a C-funtion to compute the azimuth of a LSEG but the function
> never
> returns the correct value, but elog( ... ) report the correct value.
> So there seems to be a problem returning doubles or floats ??
> 
> compile the folling function with
> gcc -fPIC -O2 -shared  -o lseg_azimuth.o -c lseg_azimuth.c
> -I/opt/local/postgres/include -L/opt/local/postgres/lib
> ld -G -Bdynamic -o libgeom.so   lseg_azimuth.o 
> 
> #include <math.h>
> 
> #include "postgres.h"
> #include "utils/geo_decls.h"
> 
> double lseg_azimuth( LSEG* lseg );
> float add_one( float arg );
> 
> double lseg_azimuth( LSEG* lseg )
> {
>   double x1, y1;
>   double x2, y2;
>   double ori;
> 
>   x1 = lseg->p[0].x;
>   y1 = lseg->p[0].y;
> 
>   x2 = lseg->p[1].x;
>   y2 = lseg->p[1].y;
> 
>   ori = atan2( (x2-x1), (y2-y1));
>   ori = (ori / M_PI) * 200.0;
> 
>   if ( ori < 0.0 )
>     ori += 400.0;
> 
>   elog( NOTICE, "ori = %8.3lf", ori );
> 
>   return( ori );  
> }

(See in PgSQL source code src/backend/utils/adt/ and geo routines).

Try this:

double*
lseg_azimuth( LSEG* lseg )
{double *result = (double) palloc(sizeof(double));    
......
*result = any_value;    
......return result;
}                        Karel                    

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Karel Zak <zakkr@zf.jcu.cz>                      http://home.zf.jcu.cz/~zakkr/

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