ios - How to convert unix timestamp to NSData object? -

i'm using core bluetooth write peripheral. send current unix timestamp sensor, , have attempted so:

// write timestamp paired peripheral nsdate*           measuretime = [nsdate date]; nsdateformatter*  usdateformatter = [nsdateformatter new]; nslocale*         enusposixlocale = [[nslocale alloc] initwithlocaleidentifier:@"en_us_posix"];  [usdateformatter setdateformat:@"yyyy-mm-dd't'hh:mm:ss.000'z'"]; [usdateformatter settimezone:[nstimezone timezonewithabbreviation:@"utc"]]; [usdateformatter setlocale:enusposixlocale];  // should force 24hr time regardless of settings value  nsstring *datestring = [usdateformatter stringfromdate:measuretime]; nsdate* starttime = [usdateformatter datefromstring:datestring];  uint32_t timestamp = [starttime timeintervalsince1970]; nsdata *timestampdata = [nsdata datawithbytes:&timestamp length:sizeof(timestamp)]; // <- troublemaker [pairedperipheral writevalue:timestampdata forcharacteristic:currentcharacteristic type:cbcharacteristicwritewithresponse]; 

here's issue:

my 32 bit timestamp returns correct value, when convert nsdata, peripheral reads 24 hour clock value this: "16:42:96"

where making error?

edit

i have modified code rid of nsdateformatter, has mentioned unnecessary. still seem getting same result:

// write timestamp paired peripheral nsdate*           measuretime = [nsdate date]; uint64_t timestamp = [measuretime timeintervalsince1970]; nsdata *timestampdata = [nsdata datawithbytes:&timestamp length:sizeof(timestamp)]; // <- troublemaker [pairedperipheral writevalue:timestampdata forcharacteristic:currentcharacteristic type:cbcharacteristicwritewithresponse];  

you confused. you're sending peripheral integer number of seconds since 1970. that's reasonable way send unix timestamp, not time in 24 hour format, integer.

you need change code use uint64_t or uint32_t since unix timestamps larger numbers fit in 32 bit integer. (i suggest using uint64_t.)

(see @donmag's comment sample timestamp values, 1491580283)

how display time once received peripheral separate question, , question should asking.

note may run problems sending int binary data if peripheral has different "endian-ness" ios device. might want convert timestamp integer string , send in order avoid endian-ness problem.