Real time clocks and reading Ports

**shoobsie** · 06-21-2005

Hi people

i am currently in Madrid Spain and working at an internship.

my task is to do some C programming.

my task is to take some information from a port on the computer (COM 3) and save it, sort it and put it into a notepad file. the info coming through is raw hex and is not very important.

the problem is that i am not sure if it possible or how to read the com port in C programming and how to put in a real time clock into the system. i have seen some theories but nothing works!! the clock is very important as at the start of every hour, a new file must created.

other wise, the sorting and rearranging i can do perfectly fine.

any help would be greatly appreciated or even a kick in the right direction!!

thanks in advance

shoobsie

**mitakeet** · 06-21-2005

Access to com ports is OS specific (sometimes compiler specific) so those details are important. Most OSs have a file-like API for com ports (open, read, write, etc.) which hide a lot of ugly detail. As for time, check out <ctime>.

**shoobsie** · 06-21-2005

thanks alot.

i managed to find something that displays the real time.

the code i will use is:

Code:

#include <stdio.h>
#include <time.h>

int main ()
{
  time_t rawtime;

  time ( &rawtime );
  printf ( "Current date and time are: %s", ctime (&rawtime) );
  
  return 0;

}

just a follow up question. is it possible to use this time for further tasks and to update it constantly?

**mitakeet** · 06-21-2005

time() on most machine only has second resolution, so calling it more than once a second will get you identical values. If you want the bits of the time value, investigate 'struct tm' and the routines that work with it (I have this stuff encapsulated in my programs, haven't looked at it in years). I have done similiar things (i.e., naming files after dates), so it is not that difficult.

**shoobsie** · 06-21-2005

once again, thank you!

i would a routine that executes the writing onto a file, once every second. with a save at the end of the hour and a new file opened up.

hence i wanted to be able to know when the clock is updated and if the program can use it to do its functions of saving and so on.

**mitakeet** · 06-21-2005

I suggest you investigate 'sleep' or on MS 'Sleep'. You can put your program in a loop checking to see if the clock has changed, but that is a total waste of CPU cycles. Sleep will allow you to ask the OS to wake your program up at a certain time (it is NOT required to!) and your program uses no cycles when that is happening. If you want to write to the file AND detect that the time has changed, you will probably need to learn to multi-thread.

**Codeplug** · 06-21-2005

shoobsie - what OS and compiler are you using? If we know that, we can point you to specific resources.

gg

**shoobsie** · 06-21-2005

guys, i´m using windows 2000 pro
and Microsoft Visual C++ 6

thanks to those who have helped

**Codeplug** · 06-21-2005

Serial Communications in Win32

If you don't mind using C++, I've posted a wrapper class for performing serial communications here: http://cboard.cprogramming.com/showthread.php?t=47870

As for doing something every second, calling Sleep(1000) will be the easiest way to get you started.

gg

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