(LFS) Allow files whose sizes cannot be represented in an off_t (but can be represented in an off64_t) to be opened. The _LARGEFILE64_SOURCE macro must be defined (before including any header files) in order to obtain this definition. Setting the _FILE_OFFSET_BITS feature test macro to 64 (rather than using +o-largefile+) is the preferred method of accessing large files on 32-bit systems (see feature_test_macros(7)).