Create new files, whose name depends on a variable from the program

Question

I'm trying to write a program that will save "X" number of simple textfiles- however, X is determined by the user once the program has run. I can't seem to find any help on the net as to how to solve the following two things, so any tips will be massively appreciated!

1) How do I declare these textfiles at the start of the program if I don't know how many there will be?

• So far, I'm used to using:

  FILE* outfile;
  

• But what I really need is:

  FILE* outfile_0, outfile_1, outfile_2... outfile_X;
  

• The solution that comes to mind looks like a loop, but I know that this won't work!

  for (i=0;I<X;i++){
      FILE* outfile_i     // obviously, this just literally calls it "outfile_i" 
  }
  

2) How do I name them?

• I want to call them simple names, such as "textfile_1, textfile_2" etc, but I don't see how that would be possible using:

  outfile=fopen("C:\\textfile.txt","w");
  

• Again, I thought perhaps making a loop (?!) but I know that this won't work:

  for(i=0;i<X;i++){
      outfile_i=fopen("C:\\textfile_i.txt","w");
  }
  

There's absolutely no way of knowing what variable "X" is before running the program.

EDIT: Problem solved- I wasn't aware you could create arrays of "FILE*", thanks for all the help!

Answer 1

You have to put all your FILE * variables in an array. I would do:

char filename[80];
char number[10];

/* Allocate our array */
FILE ** files = malloc((sizeof(FILE *) * X) + 1); /* We allocate a size of X+1 because we'll have X elements + a last NULL element. */

/* Populate our array */
for (int i = 0; i < X; i++)
{
    strcpy(filename,"C:\\textfile_");
    itoa(i, number, 10); /* Here 10 means we use decimal base to convert the integral value. */
    strcat(filename, number);
    strcat(filename, ".txt");

    files[i] = fopen(filename, "w");
}
files[i] = NULL; /* Here we set the last element of our array to NULL (so when we iterate over it we can stop when we encounter NULL). */

Then you can access all your files like this:

for (int i = 0; files[i] != NULL; i++)
{
    FILE * current = files[i];
    /* Do something with "current" here. */
}

---

PS: Some security checks are required:
malloc → Verify it doesn't return NULL.
itoa → Verify that output string is valid.
fopen → Verify that the file was opened.

Answer 2

Something like this should work, but requires error handling and close/free operations.

FILE **outfile = malloc(sizeof(FILE*) * X);
for(i=0;i<X;i++){
    char buffer[1024];
    sprintf(buffer, "%s_%d.txt", "textfile", i);
    outfile[i] = fopen(buffer, "w");
}

Answer 3

you have to store your variables in some structure (an array, a list ...) and to create some strings in memory. For example :

#include <stdio.h>

#define X 5

int main() {
  FILE* outfiles[X];
  unsigned short i;
  char fn[32];
  for (i = 0; i < X; ++i) {
    sprintf(fn, "outfile_%u", i);
    outfiles[i] = fopen(fn, "w");
  }
}

Answer 4

Try this-

char buffer[100];
FILE* outfile[X];
for(i=0;i<X;i++){
snprintf(buffer,100,"C:\\textfile_%d.txt",i);

outfile[X]=fopen(buffer,"w");
}

Answer 5

This should help you.

# include <stdio.h>
# include <string.h>
int main ()
{
    char *textfile;
    int i, X;
    textfile = (char *) malloc (128 * sizeof (char));
    FILE *fptr;
    printf ("Enter the value of X: ");
    scanf ("%d", &X);
    for (i=1 ; i<=X ; i++)
    { 
        sprintf(textfile, "textfile_%d.txt", i);
        fptr = fopen (textfile, "w");
        fclose (fptr);
    }
    return 0;
}