How to use index in the file name

Question

This is probably trivial question. I am not a professional programmer, I am rather a mathematician who is doing some numerical experiment using C. I would like the output of my

Answer 1

Use sprintf to generate the filename.

char buf[80];
sprintf(buf,"file%d", i);
fopen(buf,"w");

Array syntax in C uses square brackets [].

Answer 2

In C, use snprintf:

char buf[PATH_MAX];
snprintf(buf, sizeof(buf), "file%d", i);

If you use linux, there is a useful GNU extension:

char *name;
asprintf(&name. "file%d", i);

You need to remember to free(name) after use.

Note that your syntax FILE *f(i); is not valid though.

If you need to declare an array of FILE * of 10 elements do:

FILE *array[10];

then use it like that:

array[i] = fopen(filename, "W");

Answer 3

You could try this:

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

int main(void) {

   int i = 0;
   for (i = 0; i < 10; i++) {
      char filename[64];
      sprintf(filename, "file%d", i);    
      FILE *fp = fopen(filename, "w");
      fprintf(fp, "%d\n", i);
      fclose(fp);
   }
   return 0;
}

Your code is almost ok. Some observations:

• Use sprintf to create the name of the file. In C there is not a concatenate operator of strings.
• You don't need to create an array of file pointers.
• And of course, this may be improved: handling the size of the filename, padding the numbers, etc.

Answer 4

You can just build a string up with sprintf. Make sure your buffer is large enough:

char filename[20];
sprintf( filename, "file%d", i );

Then you can open it like this:

FILE *f = fopen( filename, "w");
...
fclose(f);

No need to use an array (if that's what you were trying to do with f(i)), because you're only keeping one file open at a time.

If you want your files to be text-sortable, you might want file001, file002 etc... You can use %03d instead of %d to 0-pad to 3 digits.