✘example

[Gary E. Miller]

Yo All!

This issue keeps coming up:

https://gitlab.com/gpsd/gpsd/-/issues/126

I think the source is several Stackoverflow answers that totally
misunderstand gpsd.  Looking at one of them, they make the valid
complaint that the libgps man page does not have a working example.

I think I have a minimal one.  I include in inline below, and as an
attachment for anyone that gets it munge by email.

I started to add comments, and it became way too large for a man page.
So I'm considering puting this in the libgps man page, and then
writing a more detailed white paper on the subject.

Comments?

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        gem@rellim.com  Tel:+1 541 382 8588

            Veritas liberabit vos. -- Quid est veritas?
    "If you can't measure it, you can't improve it." - Lord Kelvin


// example  gpsd client
// compile this way:
//    gcc example .c -o example -lgps -lm
#include <gps.h>
#include <math.h>        // for isfinite()
#include <unistd.h>      // for sleep()

#define MODE_STR_NUM 4
char *mode_str[MODE_STR_NUM] = {
    "n/a",
    "None",
    "2D",
    "3D"
};

int main(int argc, char *argv[])
{
    struct gps_data_t gps_data;

    if ( 0 != gps_open("localhost", "2947", &gps_data)) {
        printf("Open error.  Bye, bye\n");
        return 1;
    }

    (void)gps_stream(&gps_data, WATCH_ENABLE | WATCH_JSON, NULL);

    while (gps_waiting(&gps_data, 5000000)) {
        if (gps_read(&gps_data, NULL, 0) == -1) {
            printf("Read error.  Bye, bye\n");
            break;
        } 
        if (MODE_SET != (MODE_SET & gps_data.set)) {
            // did not even get mode, nothing to see here
            continue;
        }
        if (0 > gps_data.fix.mode || MODE_STR_NUM <= gps_data.fix.mode) {
            gps_data.fix.mode = 0;
        }
        printf("Fix mode: %s (%d) Time: ",
               mode_str[gps_data.fix.mode],
               gps_data.fix.mode);
        if (TIME_SET == (TIME_SET & gps_data.set)) {
            // not 32 bit safe
            printf("%ld.%09ld ", gps_data.fix.time.tv_sec,
                   gps_data.fix.time.tv_nsec);
        } else {
            puts("n/a ");
        }
        if (isfinite(gps_data.fix.latitude) &&
            isfinite( gps_data.fix.longitude)) {
            // Display data from the GPS receiver if valid.
            printf("Lat %.6f Lon %.6f\n",
                   gps_data.fix.latitude, gps_data.fix.longitude);
        }
    }

    /* When you are done... */
    (void)gps_stream(&gps_data, WATCH_DISABLE, NULL);
    (void)gps_close(&gps_data);
    return 0;
}

example.c
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pgpIKcR7R_Vnd.pgp
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