Defined in header <filesystem> | ||
enumclass perms; | (since C++17) | |
This type represents file access permissions.
perms satisfies the requirements ofBitmaskType (which means the bitwise operatorsoperator&,operator|,operator^,operator~,operator&=,operator|=, andoperator^= are defined for this type).none represents the empty bitmask; every other enumerator represents a distinct bitmask element.
Access permissions modelPOSIX permission bits, and any individual file permissions (as reported byfilesystem::status) are a combination of some of the following bits:
Contents |
| 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 toowner_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 togroup_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 toothers_read| others_write| others_exec |
all | 0777 | All users have read, write, and execute/search permissions Equivalent toowner_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 toall| 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. whenfilesystem::file_status is created without permissions) |
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).
#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--
(C++17)(C++17) | determines file attributes determines file attributes, checking the symlink target (function)[edit] |
(C++17) | modifies file access permissions (function)[edit] |
