the size and alignment of struct hsearch_data are matched to the glibc definition for binary compatibility. the members of the structure do not match, which should not be a problem as long as applications correctly treat the structure as opaque. unlike the glibc implementation, this version of hcreate_r does not require the caller to zero-fill the structure before use.
the old behavior of exposing nothing except plain ISO C can be obtained by defining __STRICT_ANSI__ or using a compiler option (such as -std=c99) that predefines it. the new default featureset is POSIX with XSI plus _BSD_SOURCE. any explicit feature test macros will inhibit the default. installation docs have also been updated to reflect this change.
to deal with the fact that the public headers may be used with pre-c99 compilers, __restrict is used in place of restrict, and defined appropriately for any supported compiler. we also avoid the form [restrict] since older versions of gcc rejected it due to a bug in the original c99 standard, and instead use the form *restrict.