Changes

NSFileHandle objects maintain a pointer to the current position in a file. This is referred to as the ''offset''. When a file is first opened the offset is set to 0(the beginning of the file). This means that any read or write operations we perform using the NSFileHandle methods will take place at offset 0 in the file. To perform operations at different locations in a file (for example to append data to the end of the file) it is first necessary to ''seek'' to the required offset. For example to move the current offset to the end of the file, use the ''seekToEndOfFile'' method. Alternatively, ''seekToFileOffset'' allows you to specifiy the precise location in the file to which the offset is to be positioned. Finally, the current offset may be identified using the ''offsetInFile'' method. in order to accommodate large files, the offset is stored in the form of an unsigned long long.