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std::experimental::filesystem::perms

From cppreference.com
< cpp‎ | experimental‎ | fs
 
 
Technical specifications
Filesystem library (filesystem TS)
Library fundamentals (library fundamentals TS)
Library fundamentals 2 (library fundamentals 2 TS)
Extensions for parallelism (parallelism TS)
Extensions for concurrency (concurrency TS)
Concepts (concepts TS)
Ranges (ranges TS)
Special mathematical functions (special math TR)
 
 
Defined in header <experimental/filesystem>
enum class perms;
(filesystem TS)

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)

Access permissions model POSIX permission bits, and any individual file permissions (as reported by status) are a combination of some of the following bits:

Contents

[edit] 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
owner_all 0700 S_IRWXU File owner has read, write, and execute/search permissions

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
group_all 070 S_IRWXG The file's user group has read, write, and execute/search permissions

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
others_all 07 S_IRWXO Other users have read, write, and execute/search permissions

Equivalent to others_read | others_write | others_exec

all 0777 All users have read, write, and execute/search permissions

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
sticky_bit 01000 S_ISVTX Implementation-defined meaning, but POSIX XSI specifies that when set on a directory, only file owners may delete files even if the directory is writeable to others (used with /tmp)
mask 07777 All valid permission bits.

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 file_status is created without permissions)
add_perms 0x10000 Control bit that instructs permissions to add, but not clear permission bits.
remove_perms 0x20000 Control bit that instructs permissions to clear, but not add permission bits
resolve_symlinks 0x40000 Control bit that instructs permissions to resolve symlinks

[edit] 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)

[edit] Example

#include <fstream>
#include <bitset>
#include <iostream>
#include <experimental/filesystem>
namespace fs = std::experimental::filesystem;
 
void demo_perms(fs::perms p)
{
     std::cout << ((p & fs::perms::owner_read) != fs::perms::none ? "r" : "-")
              << ((p & fs::perms::owner_write) != fs::perms::none ? "w" : "-")
              << ((p & fs::perms::owner_exec) != fs::perms::none ? "x" : "-")
              << ((p & fs::perms::group_read) != fs::perms::none ? "r" : "-")
              << ((p & fs::perms::group_write) != fs::perms::none ? "w" : "-")
              << ((p & fs::perms::group_exec) != fs::perms::none ? "x" : "-")
              << ((p & fs::perms::others_read) != fs::perms::none ? "r" : "-")
              << ((p & fs::perms::others_write) != fs::perms::none ? "w" : "-")
              << ((p & fs::perms::others_exec) != fs::perms::none ? "x" : "-")
              << '\n';
}
 
int main()
{
    std::ofstream("test.txt"); // create file
 
    std::cout << "Created file with permissions: ";
    demo_perms(fs::status("test.txt").permissions());
 
    fs::permissions("test.txt", fs::perms::add_perms |
                                fs::perms::owner_all | fs::perms::group_all);
 
    std::cout << "After adding o+rwx and g+rwx:  ";
    demo_perms(fs::status("test.txt").permissions());
 
    fs::remove("test.txt");
}

Possible output:

Created file with permissions: rw-r--r--
After adding o+rwx and g+rwx:  rwxrwxr--

[edit] See also

determines file attributes
determines file attributes, checking the symlink target
(function) [edit]
modifies file access permissions
(function) [edit]