Thread: file naming problem

I am not trolling and nor is this trying to complement the other thread I made.

it is a genuine and real issue I am facing and worth starting a new thread - since it is very instructional.

I just hope this does not become another hydra problem.

So here is the issue. Suppose there is a very big file full of data. Total of 100,000 rows of data, in 3 columns.
Now suppose those 10k rows actually are in 100 groups of data, each group/block is 1000 rows.


So now i have to write a program that reads this one big file full of 100k rows of data, and then write it in 100 separate files.

question is how to declare the file name - the crude way is to open 100 files, each named successively as 0.dat, 1.dat, 2. dat and so on.

The other is to have some kind of running variable that will achieve this - however when i try -

Code:

fp2 = fopen (x".dat", "w");

where x is the variable that stores the file number.

However it is not working - can someone pls suggest -

my guess it that i should start two loops

the outer loop, i, going from 0 to 99
the inner loop, j, going from 0 to 1000

There has to be a pointer, say *x, that stores the value of i and then i should name the files like this -

Code:

fp2 = fopen (x".dat", "w");

a tricky problem !!

Originally Posted by but

a tricky problem !!

A very simple problem, actually.

Code:

#include <stdio.h>

int main(void) {
    char line[2000];
    FILE *fpin = fopen("inputfile", "r");
    for (int i = 0; i < 100; i++) {
        FILE *fpout;
        char filename[32];
        sprintf(filename, "%d.dat", i);  // or "%03.dat" to pad with zeroes
        fpout = fopen(filename, "w");
        for (int j = 0; j < 1000; j++) {
            fgets(line, sizeof line, fpin);
            fputs(line, fpout);
        }
        fclose(fpout);
    }
    fclose(fpin);
    return 0;
}

Originally Posted by but

Pls let me know if the comments i made are right or if i misunderstood your code.

Yes your comments are correct. And it should be quite simple for you to add the new functionality to your old code. If you're having trouble, post your attempt.

sure - here it is

Code:

 int i, j;
 double x, y, z;
 char line[4096];
 FILE *fp;
 fp = fopen ("abcd.gro", "r"); //  reading  
 for (j=1; j<3; j++)
     {
       FILE *fp2;
       char filename[32];
       sprintf(filename, "%d.dat",j);
       fp2 = fopen(filename, "w");
       fgets(line, sizeof line, fp);
       fgets(line, sizeof line, fp);
       for (i=0; i<13968; i++)
       {
        fgets(line, sizeof line, fp);
        if (sscanf(line, "%*f %*f %lf %lf %lf", &x, &y, &z) != 3)
        {
        printf("bad line: j=%d i=%d\[%s]\n", j, i, line);
        //return EXIT_FALIURE;
        }
        if (i%4 != 3)//i need to print all but every 4th line
            fprintf(fp2, "%.5f %.5f %.5f\n", x, y, z);
          }
     fgets(line, sizeof line, fp);
     fclose(fp2);
      }

and it works - but i didnt entirely get what you did.

Sometimes I add a time stamp to the filename, but in this case a simple count would work as others have suggested.