C program time stamp in hh:mm:ss.xxx millisecond and file handling issue

Question

I am currently doing a research project on VANETs (vehicular Ad hoc networks). I am using 4 laptops installed with ubuntu 12. and above. So, my GPS displays the time stamp in the format (hh:mm:ss.xxx) where xxx is the millisecond. I have tried using gettimeofday() and other date and time functions, but none seems to give me the same required time format output. nevertheless the command on the terminal ( date +"%T.%3N") gives me the exact format as mentioned above. Since, I need this output to be saved in an external file. I have tried using a bash script inside my c program. But I am unable to print a new line in the file from the main using file handling fopen() to insert a new line in the file.

Using this code. I was able to print the time in required format in the file(datebash.csv) , but the problem is that I need to add new line to the same file from the main() using file pointer. But the new line is not getting added to the file and the time is being printed in the same line of the datebash.csv file.

My C program is as follows:

#include <stdio.h>
#include <stdlib.h>
#include <sys/timeb.h>

#define SHELLSCRIPT "\
#/bin/bash \n\
now=$(date +'%T.%3N') \n\
printf \"$now \" >> datebash.csv \n\
printf \" \" >> datebash.csv \n\
"

    int main()
    {
        int i,a=3,b=3,j;
        FILE *fp;
        puts("Will execute sh with the following script :");
        puts(SHELLSCRIPT);
        puts("Starting now:");
        system(SHELLSCRIPT); // calls the bash script above and runs(SHELLSCRIPT)

        for(i=0;i<300;i++) // just to have a few milliseconds to lapse doing this loop
        { a+b*100;}

        system(SHELLSCRIPT); // calls the bash script again and prints the result in the same file(datebash.csv)

        fp = fopen ("datebash.csv", "a+ ");   // I am opening from here the same file datebash.csv so That I can print a new line to it.
           if(fp==NULL)
            {
                printf("Error!");   
                exit(1); 
            }

        fseek(fp,0,SEEK_END); // placing cursor at end of file to insert new line here
           fprintf(fp ,"\n"); //printing new line

        system(SHELLSCRIPT);***//the problem is here.. the new line is not getting printed in the datebash.csv when the function is called from here. the time is getting printed in the first line itself.***

        return 0;
    }

Thanks

can you show us your current progress? – Sourav Ghosh Nov 06 '14 at 05:49 — Sourav Ghosh, Nov 06 '14 at 05:49
the above is my simple code @Sourav Ghosh – Shezwan91 Nov 06 '14 at 07:44 — Shezwan91, Nov 06 '14 at 07:44

score 0 · Answer 1 · edited Nov 06 '14 at 06:48

If I understand, you want to write to a file, with a time stamp, followed by a , followed by another time stamp. and you want to gen the time stamps via date+"%T.%3N on your terminal.

on your terminal:::

( date +"%T.%3N") >> file.csv

However, if you want to write a program to do so (pseudo code)

fn = open( "file.csv", O_append, S_iwrite );
check that open was successful, I.E. fn >= 0
if ( 0 <= fn ) // actually, expect fn to be greater than 2
{
    char buffer[30] = {0};

    while(1) 
    {
        read GPS value into buffer
        write ( fn,  buffer,  strlen(buffer)  );
        fflush( fn );
        memset( buffer, 0x00, sizeof buffer );
        strcat( buffer, " ,"); 
        // if the reading of the GPS value is not self pacing, then 
        // use sleep(5); or something similar here
    }
}

you probably want to add some way to close the file upon program exit

thanks.. but i am able to get the gps time and system just fine with my new code. the problem now is trying to insert new line or space inside the file (datebash.csv) from the main() — Shezwan91, Nov 06 '14 at 07:20

C program time stamp in hh:mm:ss.xxx millisecond and file handling issue

1 Answers1