C: What's the right data type to use for file sizes in bytes?

Question

If I use something like double to hold file sizes in bytes, this will naturally fail very soon, so which data type would I use? Nowadays a couple of TB are common, so I'd like the data type to be able to hold a number that big.

Answer 1

It will depends on you platform. On Unix System, you can probably use the off_t type. On Windows, you'll probably want to use LARGE_INTEGER. Those are the types used on those system by the function returning the file size (stat on Unix, GetFileSize on Windows).

If you want a portable type, uint64_t should be large enough.

Answer 2

There is a function called ftello() which returns a off_t.

With fgetpos(), you need a fpos_t variable - EDIT: which is not necessarily an arithmetic type.

So off_t could/should be appropriate to fit your needs, and keeps you independent of the actual data type sizes.