I use these commands " $fopen(fp) &  $fstrobe(fp, ...) & $fclose(fp)" to write the output periods of a PLL into a file. I made a transient simulation, like as 30us, If I set
"if $abstime>=25us; $fclose(fp)" .  The output results are continue written into the file, even if the file is already closed. The number of the written output periods seems to be not dependent of the close time, just only dependent on  the whole transient simulation time.
what is the problem???

Ken, Thanks for your help! Indeed, I donot want to write the periods into the file any more after it is closed.  The verlioga code is showed in following:
......
@(initial_step)begin
         fp=$fopen("PLLPeriods.tcl","w");
   end
@(cross((V(VCO_out)-v_th),1)) begin
         if ($abstime>=tstart) $fstrobe(fp,"%3.10e",$abstime-prev);
     prev=$abstime;
end
if($abstime >= tclose) $fclose(fp);
end
endmodule

Something wrong in the code ?  :P
This problem is not very serious. More samples periods is not a bad thing.

Ken, thanks for your answer!
From my understanding, the periods should begin to be written into the file at the time point "tstart", and then couldn't be written into the file after the time point "tclose".  What do the Spectre actually do? I don't know?
your metioned another condition is like this "if ($abstime>=tstart)&&($tstart<=tend) then $fstrobe..." ?.
But without $fclose(fp), if i do a simulation again, the new simulation results would append the last simualtion results. That isn't what i want to get.
you can see my last question. http://www.designers-guide.org/Forum/?board=verilogams;action=display;num=112559...

You can use the @(final_step) event to close the file.

-Ken

Ken, thanks!

This is a good suggestion to close the file at the end of simualtion. But i am still strange when the file is already closed, how can the Spectre wirte data into the file?

I am sure I have closed the file, otherwise the new simualtion results would append to the old results.
I have tried to use  "$fstrobe(fp,"closing file"), $fclose(fp)" . The output file looks like
"
....
close file
close file
4.032424e-9         // this is output period
clese fiile
....
"
It might  be a small bug. 8)
Anyway, the Ken's suggestion is good way to close the file.