This function writes the user entry
*p to the stream stream, in the format used for the standard user database file. The return value is zero on success and nonzero on failure.
This function exists for compatibility with SVID. We recommend that you avoid using it, because it makes sense only on the assumption that the
struct passwdstructure has no members except the standard ones; on a system which merges the traditional Unix data base with other extended information about users, adding an entry using this function would inevitably leave out much of the important information.
putpwentis declared in pwd.h.