reading a file of unknown length

hey people!!

Need a little help if someone has five minutes.
I'm trying to write some code to read from a file, without
knowing the exact length of the file, if you know what i mean.

This is what i've come up with.

Code:

---




#include<stdio.h>
#include<stdlib.h>
FILE*fptr;

main()
{
    int i;
    char *m[5];
    char why[16];
 
    fptr=fopen("c:\\MYTEST ", "w+");
    fprintf(fptr,"hello to whole world...whats goin down in happyville??\n");
    fseek(fptr, 0, SEEK_SET);
    while(!feof(fptr))
    {
    gets(why);
        if(!feof(fptr))
        {
            for(i=0;i<5;i++)
            {
                m[i]= (char*) malloc(10*1);
            }
        }
    }
   
        printf("%s %s %s %s %s %s", why,m[0],m[1],m[2],m[3],m[4]);
       
            fclose(fptr);
           
                getchar();
            }

---

this code doesnt actually work, hence my call for help. The creation of
the file works however when it gets to the 'while' something must go wrong
because my command window just shows a blank.


i'm sure its obvious that i'm a little new to this and
i'm probably trying to run before i can walk but if someone can give
me a little insight into how this sort of thing is done
i'd be real greatful

It doesn't actually matter how big a file is if you work line-by-line. Lots of people recommend trying it this way first, before doing anything dramatic, if you have a more complex file to read.

The easiest way to read a line from a file is actually to put fgets in a loop. feof() shouldn't be used in a while loop.

Code:

---

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

int main (void) {
  FILE * txtin;
  txtin = fopen("junk.txt", "a+");
  if (txtin != NULL) {
      fputs("SAGE - set a good example", txtin);
      char buf[BUFSIZ] = {'\0'};
      /* one of your biggest responsibilities is just supplying big
      * enough storage space
      */
      while (fgets(buf, BUFSIZ, txtin) != NULL) {
          /* buf now contains a line... do your processing,
          * whatever it may be.
          */
          fputs(buf, stdout);
      }
  } else {
      perror("fopen");
  }

  fclose(txtin);
  return 0;
}

---

For the sake of example this just outputs the contents of the file onto the screen, but this snippet is particularly common I believe.

Reference:
http://www.cprogramming.com/tutorial/cfileio.html
http://faq.cprogramming.com/cgi-bin/...&id=1043284385
http://faq.cprogramming.com/cgi-bin/...&id=1043284351

Have a look at the FAQ for a few items that you might want to clear up in your code:

Why gets() is bad / Buffer Overflows
Casting malloc
Why it's bad to use feof() to control a loop

Also, when you call malloc, you ought to make an attempt to free the allocated memory when you are done with it.