c++ - Setting system time with gps timestamp_t structure in Linux -

setting system time gps timestamp_t structure in linux

hi everyone,

i'm trying write code succesfull gps lock (adafruit ultimate gps w/ gpsd) set system time. right now, can see 'timestamp_t':

typedef double timestamp_t; /* unix time in seconds fractional part */ 

is part of "gps_data_t*" structure. start, however, function planned on using set system time in linux is:

int settimeofday(const struct timeval *tv, const struct timezone *tz); 

i've found information on how convert time_t *timeval, how should handle double convert *timeval?

code:

gpsmm gps_rec("localhost", default_gpsd_port);  if (gps_rec.stream(watch_enable|watch_json) == null) {     std::cout << "no gpsd running. exiting gps thread." << std::endl;     return; }  //data structure struct gps_data_t* newdata;  //loop until first gps lock set system time while ((newdata = gps_rec.read()) == null) {     //wait valid read }  //set system time - timestamp_t vs timeval? timeval *tv{?? newdata->time ??}; timezone *tz{ timezone(300, dst_usa)}; settimeofday(tv, tz); 

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some comments , links have helped me. confusion differentiating between timeval, time_t, , timestamp_t. understand here differences, please correct if not case:

all time in seconds after jan 1st, 1970, but...

timeval structure of (2) long values, tv_sec seconds after 1/1/1970, tv_usec microseconds after that.

time_t long? seconds after 1/1/1970

timestamp_t double seconds after 1/1/1970, decimal part calculate microseconds 'roughly' same precision of timeval.

so conversion between of them go such:

timeval time; time_t timet; timestamp_t timestampt;  timet = time.tv_sec;   //usec dropped timet = timestampt;    //usec dropped timestampt = timet;    //usec not given timestampt = time.tv_sec; timestampt += (time.tv_usec / 1000000)  //denominator may off few 0's 

is painting clearer picture?

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to go opposite way, needed application:

//convert gps_data_t* member 'time' timeval timeval tv; double wholeseconds, decimalseconds; decimalseconds = modf(newdata->time, &wholeseconds); tv.sec = static_cast<int32_t>(wholeseconds); tv.usec = static_cast<int32_t>(decimalseconds * 1000000.0);  //create timezone timezone tz{ timezone(300, dst_usa)};  //set system time settimeofday(&tv, &tz); 

here is:

//get first data set system time struct gps_data_t* firstdata;  //loop until first gps lock set system time while (((firstdata = gps_rec.read()) == null) ||         (firstdata->fix.mode < 1)) {     //do nothing }  //convert gps_data_t* member 'time' timeval timeval tv; double wholeseconds, decimalseconds, offsettime; offsettime = firstdata->fix.time - (5.0 * 3600.0);  //5hr offset gmt decimalseconds = modf(offsettime, &wholeseconds); tv.tv_sec = static_cast<int32_t>(wholeseconds); tv.tv_usec = static_cast<int32_t>(decimalseconds * 1000000.0);  //set system time if ( settimeofday(&tv, null) >= 0) {     std::cout << "time set succesful!" << '\n'; } else {     std::cout << "time set failure!" << '\n'; }