Changes access permissions of the file to whichp resolves, as if by POSIXfchmodat. Symlinks are followed unlessperm_options::nofollow is set inopts.

The second signature behaves as if called withopts set toperm_options::replace.

The effects depend onprms andopts as follows:

• Ifopts isperm_options::replace, file permissions are set to exactlyprms&std::filesystem::perms::mask (meaning, every valid bit ofprms is applied).
• Ifopts isperm_options::add, the file permissions are set to exactlystatus(p).permissions()|(prms& perms::mask) (meaning, any valid bit that is set inprms, but not in the file's current permissions is added to the file's permissions).
• Ifopts isperm_options::remove, the file permissions are set to exactlystatus(p).permissions()& ~(prms& perms::mask) (meaning, any valid bit that is clear inprms, but set in the file's current permissions is cleared in the file's permissions).

opts is required to have only one ofreplace,add, orremove to be set.

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

[edit]Parameters

[edit]Return value

(none)

[edit]Exceptions

Any overload not markednoexcept may throwstd::bad_alloc if memory allocation fails.

[edit]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).

[edit]Example

#include <filesystem>#include <fstream>#include <iostream> void demo_perms(std::filesystem::perms p){usingstd::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--

[edit]See also

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