std::experimental::filesystem::perms

 

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Technical Specifications

 

Technical specifications

Filesystem library (filesystem TS)

Library fundamentals (library fundamentals TS)

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Filesystem library

Classes
filesystem::path filesystem::filesystem_error filesystem::directory_entry filesystem::directory_iterator filesystem::recursive_directory_iterator filesystem::file_status	filesystem::space_info filesystem::file_type filesystem::perms filesystem::copy_options filesystem::directory_options filesystem::file_time_type
Functions
filesystem::absolute filesystem::system_complete filesystem::canonical filesystem::copy filesystem::copy_file filesystem::copy_symlink filesystem::create_directory filesystem::create_directories filesystem::create_hard_link filesystem::create_symlink filesystem::create_directory_symlink filesystem::current_path filesystem::exists filesystem::equivalent	filesystem::file_size filesystem::hard_link_count filesystem::last_write_time filesystem::permissions filesystem::read_symlink filesystem::remove filesystem::remove_all filesystem::rename filesystem::resize_file filesystem::space filesystem::status filesystem::symlink_status filesystem::temp_directory_path
File types
filesystem::is_block_file filesystem::is_character_file filesystem::is_directory filesystem::is_empty filesystem::status_known	filesystem::is_fifo filesystem::is_other filesystem::is_regular_file filesystem::is_socket filesystem::is_symlink

 

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:

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

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 <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 ? "r" : "-")
              << (p & fs::perms::owner_write ? "w" : "-")
              << (p & fs::perms::owner_exec ? "x" : "-")
              << (p & fs::perms::group_read ? "r" : "-")
              << (p & fs::perms::group_write ? "w" : "-")
              << (p & fs::perms::group_exec ? "x" : "-")
              << (p & fs::perms::others_read ? "r" : "-")
              << (p & fs::perms::others_write ? "w" : "-")
              << (p & fs::perms::others_exec ? "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+wrx:  ";
    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+wrx:  rwxrwxr--

See also

statussymlink_status	determines file attributes determines file attributes, checking the symlink target (function)
permissions	modifies file access permissions (function)