#include <gps.h>
int gps_open(char * server, char * port, struct gps_data_t * gpsdata)
int gps_send(struct gps_data_t * gpsdata, char * fmt, ...)
int gps_read(struct gps_data_t * gpsdata, char * message,
             int message_size)
bool gps_waiting(const struct gps_data_t * gpsdata, int timeout)
char * gps_data(const struct gps_data_t * gpsdata)
int gps_unpack(char * buf, struct gps_data_t * gpsdata)
int gps_close(struct gps_data_t * gpsdata)
int gps_stream(struct gps_data_t * gpsdata, unsigned int flags,
               void * data)
int gps_mainloop(struct gps_data_t * gpsdata, int timeout,
                 void (* hook)(struct gps_data_t *gpsdata))
const char * gps_errstr(int err)

import gps
session = gps.gps(host="localhost", port="2947")
session.stream(flags=gps.WATCH_JSON)
for report in session:
    process(report) del session

Warning

Take care to conditionalize your code on the major and minor API version
symbols in gps.h; ideally, force a compilation failure if GPSD_API_MAJOR_VERSION is not a version you recognize. See the GPSD project website for more information on the protocol and API changes.

Warning

gps_data_t sets floating point variables to NaN when the actual
variable value is unknown. Check all floats and doubles with isfinite() before using them. isnan() is not sufficient!

Calling gps_open() initializes a gps_data_t structure to hold the data collected by the GPS, and sets up access to gpsd(8) via either the socket or shared-memory export. The shared-memory export is faster, but does not carry information about device activation and deactivation events and will not allow you to monitor device packet traffic.

gps_open() returns 0 on success, -1 on errors and is re-entrant. errno is set depending on the error returned from the socket or shared-memory interface; see gps.h for values and explanations; also see gps_errstr(). The host address may be a DNS name, an IPv4 dotted quad, an IPV6 address, or the special value GPSD_SHARED_MEMORY referring to the shared-memory export; the library will do the right thing for any of these.

gps_close() ends the session and should only be called after a successful gps_open(). It returns 0 on success, -1 on errors. The shared-memory interface close always returns 0, whereas a socket close can result in an error. For a socket close error it will have set an errno from the call to the system’s close().

gps_send() writes a command to the gpsd daemon. It does nothing when using the shared-memory export. The second argument must be a format string containing elements from the command set documented at gpsd(8). It may have % elements as for sprintf(3), which will be filled in from any following arguments. This function returns a -1 if there was a Unix-level write error, otherwise 0. Please read the LIMITATIONS section for additional information and cautions. See gps_stream() as a possible alternative.

gps_read() accepts a response, or sequence of responses, from the gpsd daemon and decodes the response into a gps_data_t. By default, this function does either a blocking read for data from the gpsd daemon or a fetch from shared memory; it returns a count of bytes read for success, -1 with errno set on a Unix-level read error, -1 with errno not set if the socket to the gpsd daemon has closed or if the shared-memory segment was unavailable, and 0 if no data is available.

The second argument to gps_read() is usually NULL, and the third argument is zero. If your application wants to see the raw data from the gpsd daemon then set the second argument to the address of your message buffer, and the third argument is the size of your buffer. Use with care; this may not to be a NUL-terminated string if WATCH_RAW is enabled.

gps_waiting() can be used to check whether there is new data from the gpsd daemon. The second argument is the maximum amount of time to block (in microseconds) waiting on input before returning. It returns true if there is input waiting, false on timeout (no data waiting) or error condition. When using the socket export, this function is a convenience wrapper around a select(2) call, and zeros errno on entry; you can test errno after exit to get more information about error conditions.

Warning: under the shared-memory interface there is a tiny race window between gps_waiting() and a following gps_read(); in that context, because the latter does not block, it is probably better to write a simple read loop.

gps_mainloop() enables the provided hook function to be continually called whenever there is gpsd data. The second argument is the maximum amount of time to wait (in microseconds) on input before exiting the loop (and return a value of -1). It will also return a negative value on various errors.

gps_unpack() parses JSON from the argument buffer into the target of the session structure pointer argument. Included in case your application wishes to manage socket I/O itself.

gps_data() returns the contents of the client data buffer (it returns NULL when using the shared-memory export). Use with care; this may not to be a NUL-terminated string if WATCH_RAW is enabled.

gps_stream() asks gpsd to stream the reports it has at you, to be made available when you poll (not available when using the shared-memory export). The second argument is a flag mask that sets various policy bits; see the list below. Calling gps_stream() more than once with different flag masks is allowed.

WATCH_DEVICE

WATCH_DISABLE

WATCH_ENABLE

WATCH_JSON

WATCH_NEWSTYLE

WATCH_NMEA

WATCH_OLDSTYLE

WATCH_RARE

WATCH_RAW

WATCH_SCALED

gps_errstr() returns an ASCII string (in English) describing the error indicated by a nonzero return value from gps_open().

import gps
session = gps.gps(host="localhost", port="2947")
session.stream(flags=gps.WATCH_JSON)
for report in session:
    process(report) del session

// 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
static 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);
    // Wait for data available.
    while (gps_waiting(&gps_data, 5000000)) {
        // will not block because we know data is available.
        if (-1 == gps_read(&gps_data, NULL, 0)) {
            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;
}

•GPSD Client Example Code <https://gpsd.io/gpsd-client-example-code.html> An annotated example client.

•GPSD Client HOWTO <https://gpsd.io/client-howto.html> A GPS client HOWTO.

•Project web site: <https://gpsd.io/>