void permissions(const path& p, perms prms);
void permissions(const path& p, perms prms, error_code& ec);
Requires: !((prms & perms::add_perms) != perms::none && (prms & perms::remove_perms) != perms::none).
Effects: Applies the effective permissions bits from prms to the file p resolves to, or if that file is a symbolic link and symlink_nofollow is not set in prms, the file that it points to, as if by POSIX fchmodat(). The effective permission bits are determined as specified in Table [tab:fs.op.permissions], where s is the result of (prms & perms::symlink_nofollow) != perms::none ? symlink_status(p) : status(p).
| Bits present in prms | Effective bits applied |
| Neither add_perms nor remove_perms | prms & perms::mask |
| add_perms | s.permissions() | (prms & perms::mask) |
| remove_perms | s.permissions() & ~(prms & perms::mask) |
[ Note: Conceptually permissions are viewed as bits, but the actual implementation may use some other mechanism. — end note ]
Throws: As specified in [fs.err.report].