varied file reading

i need t read and write to files. but the problem is there are several of them, and they vary according to numbers..

for example, i need to read from r1t001, r1t002...and so on, and write to files with similar names... the second number in the file names have a buffer zeros...

i know i need variables which can change in loops, but how do i implement this in filenames and also have the buffer of zeros in the case of single, and tens of numbers..

thanks in advance!

The real question is how do you do this in char arrays; C's version of strings.

Filenames are nothing special, just plain old strings.

Look at functions such as sprintf(), strcat() etc.

thanks for that! sprintf worked..

tho sprintf attaches a '\0' to the end of the string, but i will have to delete that wouldnt i?otherwise the file operators cant handle the null character right?

Correct.

Code:

---

if ((filename[strlen(filename)-1])=='\n')
  filename[strlen(filename)-1])=='\0;'

---

Will do what you want.

This is a function that prints out data into numbered files. It's a bit different from your format, but you'll get the idea, I believe:

Code:

---

void printIt(long i, long j) {
  char fname[20];
  long k;
  FILE *fpout;
  ltoa(i, fname, 10);  //makes a long int, into a string

  strcat(fname, ".txt");  //adds the file extension I want
  printf("\nFilename: %s", fname);  //just a √
  if((fpout=fopen(fname, "w"))==NULL) {
    printf("\n Error opening level 0 output file - terminating");
    exit(1);
  }
  for(k=0;k<j;k++)        //prints out a small struct, you can ignore this part
    fprintf(fpout, "%s %s %d\n", recs[k].id, recs[k].doc, recs[k].bill);

  fclose(fpout);
}

---

Code:

---

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int n;
    int p,t;
    t = 1;
    p = 1;

    char filename[12];

    for(n=0;n<12;n++)
    {
        sprintf(filename,"p%dt%03d.state",p,t);
        printf("\n result:%s",filename);
        t = t + 1;
        n++;

    }

    return 0;
}

---

thats part of some pleriminary code i wrote...but the weird thing is, the sprintf statement seems to be resetting the "n" variable to 0, and it results in the program going into an endless loop...

and when i build, there are n errors or warnings..

what am i doing wrong?

sprintf() doesn't include the newline char in the string it writes.

Just for fun, try making filename bigger. Sounds like you're going out of bounds a bit.

Post your output to your code.

thanks for that! yeah...the filename was too small.thanks for that!