Re: diff's type used for holding line numbers

[Bruno Haible]

Andreas Gruenbacher wrote about the type used to hold line numbers in 'diff':
> > %td is for ptrdiff_t, not off_t.
> 
> Exactly, and ptrdiff_t should be machine word size, which is what we want 
> here, right?

No. ptrdiff_t may be too small.

ISO C 99 section 6.5.6.(9) says that ptrdiff_t is the type for the difference
of two pointers into the *same array*. There is no requirement that ptrdiff_t
is near the size of available RAM. For example, you can have platforms where
arrays are limited to 4 GB (or 2 GB) in size, but there is 64 GB available
RAM, and the user wants to diff two files of size 5 GB, each of them
consisting mostly of newlines. The line numbers will be > 2^32.

off_t is guaranteed to be sufficiently large, because a file cannot
contain more lines than it contains bytes on disk.

Bruno