std::filesystem::permissions

 

C++

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Technical specifications

Symbols index

External libraries

 

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::perm_options filesystem::copy_options filesystem::directory_options filesystem::file_time_type
Functions
filesystem::absolute filesystem::canonicalfilesystem::weakly_canonical filesystem::relativefilesystem::proximate 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 <filesystem>
void permissions( const std::filesystem::path& p,                   std::filesystem::perms prms,                   std::filesystem::perm_options opts = perm_options::replace );	(1)	(since C++17)
void permissions( const std::filesystem::path& p,                   std::filesystem::perms prms,                   std::error_code& ec ) noexcept;	(2)	(since C++17)
void permissions( const std::filesystem::path& p,                   std::filesystem::perms prms,                   std::filesystem::perm_options opts,                   std::error_code& ec );	(3)	(since C++17)

Changes access permissions of the file to which p resolves, as if by POSIX fchmodat. Symlinks are followed unless perm_options::nofollow is set in opts.

The second signature behaves as if called with opts set to perm_options::replace.

The effects depend on prms and opts as follows:

• If opts is perm_options::replace, file permissions are set to exactly prms & std::filesystem::perms::mask (meaning, every valid bit of prms is applied).
• If opts is perm_options::add, 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 opts is perm_options::remove, 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).

opts is required to have only one of replace, add, or remove to be set.

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

Parameters

p	-	path to examine
prms	-	permissions to set, add, or remove
opts	-	options controlling the action taken by this function
ec	-	out-parameter for error reporting in the non-throwing overload

Return value

(none)

Exceptions

Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails.

1) Throws std::filesystem::filesystem_error on underlying OS API errors, constructed with p as the first path argument and the OS error code as the error code argument.

2,3) Sets a std::error_code& parameter to the OS API error code if an OS API call fails, and executes ec.clear() if no errors occur.

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

perms (C++17)	identifies file system permissions (enum)
statussymlink_status (C++17)(C++17)	determines file attributes determines file attributes, checking the symlink target (function)