Modify one character in a string

[Marc 'BlackJack' Rintsch]

In <roy-F85321.10044225052006 at reader1.panix.com>, Roy Smith wrote:

>> Also, how do I do this when dealing with a file ; which file mode
>> should I use and what function should I use to modify a single
>> character once in that file mode?
> 
> This is a much more complicated question, because it depends on the details 
> of the operating system you're using.  On Unix, you can seek to a specific 
> place in a file, write a single character, seek to EOF, and you've done an 
> in-place single character edit of the file.

Why seeking to EOF after writing the byte?

Ciao,
	Marc 'BlackJack' Rintsch