I think it depends on what you are doing with the file.
I've found that the FILE, strtok is by far the fastest way of reading in data.
I've been using flat files, (same number of columns in all...

What is the ordering?
If you want to sort by the most frequent elements first, then you can use the link given to you.

If you are sorting by some other rule,
you should say what rule that is.

You should start by defining the problem itself.

First aff all assume you will only be using ascii symbol.
This way you will only be needing to keep track of 128 diffent kind of charachters....

Use either valgrind or gdb for finding errors.

compile with -g option
then

gdb ./yourprog
run

or
valgrind ./yourprog

I'm using unix, so I can't look at your source files,
but theres something I don't understand in you code for case2

Your are setting temp->next = null;
which probly mean that you want...

whats your platform?

Then show us the line that contains the assignment error.
And maybe even the compile error itself.

Try cutting down your program to just a few lines,
check the compile errors, fix those.
Then you should understand what you did wrong.