Programming interface to the Swiss Ephemeris - programmiastral.com

Swiss Ephemeris 4
1. The programming steps to get a planet’s position
To compute a celestial body or point with SWISSEPH, you have to do the following steps (use swetest.c as an
example). The details of the functions will be explained in the following chapters.
1. Set the directory path of the ephemeris files, e.g.:
swe_set_ephe_path(”C:\\SWEPH\\EPHE”);
2. From the birth date, compute the Julian day number:
jul_day_UT = swe_julday(year, month, day, hour, gregflag);
3. Compute a planet or other bodies:
ret_flag = swe_calc_ut(jul_day_UT, planet_no, flag, lon_lat_rad, err_msg);
or a fixed star:
ret_flag = swe_fixstar_ut(star_nam, jul_day_UT, flag, lon_lat_rad, err_msg);
Note:
The functions swe_calc_ut() and swe_fixstar_ut() were introduced with Swisseph version 1.60.
If you use a Swisseph version older than 1.60 or if you want to work with Ephemeris Time, you have to proceed as follows instead:
First, if necessary, convert Universal Time (UT) to Ephemeris Time (ET):
jul_day_ET = jul_day_UT + swe_deltat(jul_day_UT);
Then Compute a planet or other bodies:
ret_flag = swe_calc(jul_day_ET, planet_no, flag, lon_lat_rad, err_msg);
or a fixed star:
ret_flag = swe_fixstar(star_nam, jul_day_ET, flag, lon_lat_rad, err_msg);
5. At the end of your computations close all files and free memory calling swe_close();
Here is a miniature sample program, it is in the source distribution as swemini.c
#include "swephexp.h" /* this includes "sweodef.h" */
int main()
{
char *sp, sdate[AS_MAXCH], snam[40], serr[AS_MAXCH];
int jday = 1, jmon = 1, jyear = 2000;
double jut = 0.0;
double tjd_ut, te, x2[6];
long iflag, iflgret;
int p;
iflag = SEFLG_SPEED;
while (TRUE) {
printf("\nDate (d.m.y) ");
gets(sdate);
/* stop if a period . is entered */
if (*sdate == '.')
return OK;
if (sscanf (sdate, "%d%*c%d%*c%d", &jday,&jmon,&jyear) < 1) exit(1);
/*
* we have day, month and year and convert to Julian day number
*/
tjd_ut = swe_julday(jyear,jmon,jday,jut,SE_GREG_CAL);
/*
* compute Ephemeris time from Universal time by adding delta_t
* not required for Swisseph versions smaller than 1.60
*/
/* te = tjd_ut + swe_deltat(tjd_ut); */
printf("date: %02d.%02d.%d at 0:00 Universal time\n", jday, jmon, jyear);
printf("planet \tlongitude\tlatitude\tdistance\tspeed long.\n");
/*
* a loop over all planets
*/
for (p = SE_SUN; p