std::filesystem::permissions

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
• 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
• 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

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

Return value

(none)

Exceptions

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

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

#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");
}

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

See also