File pru.c:

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

main()
{
    FILE *fp;
    char a[100];

    fp=fopen("pru.c","r");
    fgets(a,100,fp);
    printf("%d\n",ftell(fp));
}

This program prints -16205 and this is a wrong file position.

That's not really a bug: just read what you find in the
description of ftell()'s companion function fseek(), and
think about what that implies. You will see quite easily
that, for almost the same reason, fseek() *can't* work on
text files.

Maybe, that should be added to libc.inf's node about ftell()?

Upgrade to v2.01, where fseek and ftell work with text files as well.