std::experimental::filesystem::permissions

 

C++

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Technical Specifications

 

Technical specifications

Filesystem library (filesystem TS)

Library fundamentals (library fundamentals TS)

Library fundamentals 2 (library fundamentals 2 TS)

Extensions for parallelism (parallelism TS)

Concepts (concepts TS)

Extensions for concurrency (concurrency TS)

 

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>
void permissions(const path& p, perms prms); void permissions(const path& p, perms prms, error_code& ec);		(filesystem TS)

Changes access permissions of the file to which p resolves, as if by POSIX fchmodat. Symlinks are followed if prms::resolve_symlinks is set.

The effects depend on prms as follows:

• If neither perms::add_perms nor perms::remove_perms is set, file permissions are set to exactly prms & fs::perms::mask (meaning, every valid bit of prms is applied)
• If perms::add_perms, the file permissions are set to exactly status(p).permissions() | (prms & perms::mask) (meaning, any valid bit that is set in prms, but not in the file's current permissions is added to the file's permissions)
• If perms::remove_perms is set, the file permissions are set to exactly status(p).permissions() & ~(prms & perms::mask) (meaning, any valid bit that is clear in prms, but set in the file's current permissions is cleared in the file's permissions)
• If both perms::add_perms and perms::remove_perms are set, error occurs

The non-throwing overload has no special action on error.

Parameters

p	-	path to examine
prms	-	permissions to set, add, or remove
ec	-	out-parameter for error reporting in the non-throwing overload

Return value

(none)

Exceptions

The overload that does not take a error_code& parameter throws filesystem_error on underlying OS API errors, constructed with p as the first argument and the OS error code as the error code argument. std::bad_alloc may be thrown if memory allocation fails. The overload taking a error_code& parameter sets it to the OS API error code if an OS API call fails, and executes ec.clear() if no errors occur. This overload has

noexcept specification:  

noexcept

  

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

perms	identifies file system permissions (enum)
statussymlink_status	determines file attributes determines file attributes, checking the symlink target (function)