How can I use clock_gettime to calculate the total time it takes for a command-CodePudding

I'm having a bit of an issue with the specifics of how to manipulate the values obtained from clock_gettime. Im looking to calculate the total running time of an executable/command.

I'm looking to print out the realtime in the format of (eg. 3.475s) I'm almost done but am pretty sure that it wont return in the format I want. How could I do so?

  struct timespec tsstart, tsend;
  clock_gettime(CLOCK_MONOTONIC, &tsstart);
  //execuatble/command executes and finishes
  clock_gettime(CLOCK_MONOTONIC, &tsend);
  long long realtime = (tsend.tv_sec-tsstart.tv_sec)*1000000LL   tsend.tv_usec-tsstart.tv_usec;
  printf("real: %.3lds, ", realtime);

Whenever I try running this, for a short period (ie. <10s), all I get is an output along the lines of

35273s

How could I change the formatting of the output to the 3d.p. precision I need ?

CodePudding user response：

  struct timespec tsstart, tsend;
  clock_gettime(CLOCK_MONOTONIC, &tsstart);
  //execuatble/command executes and finishes
  clock_gettime(CLOCK_MONOTONIC, &tsend);
  float realtime = (tsend.tv_sec-tsstart.tv_sec) (tsend.tv_nsec-tsstart.tv_nsec)/1000000000.0;
  printf("real: %.3fs, ", realtime);

CodePudding user response：

To change scaled long long integer (*1000000LL) to a x.xxxxxx output

printf("%s%lld.lld", 
    realtime < 0 ? "-" : "", 
    llabs(realtime/1000000), 
    llabs(realtime%1000000));

Tricky cases include realtime values in the the [-999999 ... -1]. Of course these values are not expected with the time subtraction.

If we assume realtime >= 0, then

printf("%lld.lld", 
    realtime/1000000, realtime%1000000);

To toss the lower 3 digits:

// Form rounded quotient of milliseconds
long long ms = realtime/1000   (realtime%1000 >= 500);
printf("%lld.lld", ms/1000, ms%1000);