Why are @, `, and $ not used in C?

[joel.ratsaby]

I have a question regarding the fseek() function.
If I open a file for the first time (let's assume the fp is now the
file descriptor), then can I fseek(fp,(any positive offset), 0) ?

I am trying to design a simple hashing algorithm, and I need to be able
to place information on the file at specific places in the file.
On the first time (after opening the file) I want to be able to seek
forward to any location from the start. Should I first write nulls
to the file (inorder to establish the length of the file)
and only then call fseek(fp,(any offset less than the max length of file),fp) ?
thanks
j.e.r