std::filesystem::perms(3)

NAME
std::filesystem::perms - std::filesystem::perms

Synopsis
   Defined in header <filesystem>
   enum class perms; (since C++17)
   This type represents file access permissions.
   perms satisfies the requirements of BitmaskType (which means the bitwise operators
   operator&, operator|, operator^, operator~, operator&=, operator|=, and operator^=
   are defined for this type). none represents the empty bitmask; every other
   enumerator represents a distinct bitmask element.
   Access permissions model POSIX permission bits, and any individual file permissions
   (as reported by filesystem::status) are a combination of some of the following bits:

Member constants
   Member constant Value (octal) POSIX equivalent Meaning
   none 0 No permission bits are set
   owner_read 0400 S_IRUSR File owner has read permission
   owner_write 0200 S_IWUSR File owner has write permission
   owner_exec 0100 S_IXUSR File owner has execute/search
                        permission
                        File owner has read, write, and
                        execute/search permissions
   owner_all 0700 S_IRWXU
                        Equivalent to owner_read |
                        owner_write | owner_exec
   group_read 040 S_IRGRP The file's user group has read
                        permission
   group_write 020 S_IWGRP The file's user group has write
                        permission
   group_exec 010 S_IXGRP The file's user group has
                        execute/search permission
                        The file's user group has read,
                        write, and execute/search permissions
   group_all 070 S_IRWXG
                        Equivalent to group_read |
                        group_write | group_exec
   others_read 04 S_IROTH Other users have read permission
   others_write 02 S_IWOTH Other users have write permission
   others_exec 01 S_IXOTH Other users have execute/search
                        permission
                        Other users have read, write, and
                        execute/search permissions
   others_all 07 S_IRWXO
                        Equivalent to others_read |
                        others_write | others_exec
                        All users have read, write, and
                        execute/search permissions
   all 0777
                        Equivalent to owner_all | group_all |
                        others_all
   set_uid 04000 S_ISUID Set user ID to file owner user ID on
                        execution
   set_gid 02000 S_ISGID Set group ID to file's user group ID
                        on execution
                        Implementation-defined meaning, but
                        POSIX XSI specifies that when set on
   sticky_bit 01000 S_ISVTX a directory, only file owners may
                        delete files even if the directory is
                        writeable to others (used with /tmp)
                        All valid permission bits.
   mask 07777
                        Equivalent to all | set_uid | set_gid
                        | sticky_bit
   Additionally, the following constants of this type are defined, which do not
   represent permissions:
   Member constant Value (hex) Meaning
   unknown 0xFFFF Unknown permissions (e.g. when filesystem::file_status
                        is created without permissions)

Notes
   Permissions may not necessarily be implemented as bits, but they are treated that
   way conceptually.
   Some permission bits may be ignored on some systems, and changing some bits may
   automatically change others (e.g. on platforms without owner/group/all distinction,
   setting any of the three write bits set all three).

Example
// Run this code
 #include <filesystem>
 #include <fstream>
 #include <iostream>
 void demo_perms(std::filesystem::perms p)
 {
     using std::filesystem::perms;
     auto show = [=](char op, perms perm)
     {
         std::cout << (perms::none == (perm & p) ? '-' : op);
     };
     show('r', perms::owner_read);
     show('w', perms::owner_write);
     show('x', perms::owner_exec);
     show('r', perms::group_read);
     show('w', perms::group_write);
     show('x', perms::group_exec);
     show('r', perms::others_read);
     show('w', perms::others_write);
     show('x', perms::others_exec);
     std::cout << '\n';
 }
 int main()
 {
     std::ofstream("test.txt"); // create file
     std::cout << "Created file with permissions: ";
     demo_perms(std::filesystem::status("test.txt").permissions());
     std::filesystem::permissions(
         "test.txt",
         std::filesystem::perms::owner_all | std::filesystem::perms::group_all,
         std::filesystem::perm_options::add
     );
     std::cout << "After adding u+rwx and g+rwx: ";
     demo_perms(std::filesystem::status("test.txt").permissions());
     std::filesystem::remove("test.txt");
 }

Possible output:
 Created file with permissions: rw-r--r--
 After adding u+rwx and g+wrx: rwxrwxr--

See also
   status determines file attributes
   symlink_status determines file attributes, checking the symlink target
   (C++17) (function)
   (C++17)
   permissions modifies file access permissions
   (C++17) (function)