CODEWITHSUNDEEP
c++linuxfile-permissionsfstream
xgord
xgord

Reputation: 4776

Setting file permissions when opening a file with ofstream

Is there a way in C++'s standard libraries (or linux sys/stat.h, sys/types.h, sys/.... libraries) to set the file permissions of a file when creating it with ofstream (or using something else from those libraries)?

When I create a file it just gets created with some default set of file permissions (I assume whatever the current umask is), but I want to explicitly set the permissions to something other than the default (ex. 600), and I can't just set the umask before starting the program (b/c others will run it). 

// Example of creating a file by writing to it
ofstream fp(filename.c_str())

/* write something to it */

Is there a way to do this in C++ or if not, a way to set the umask within the C++ program?

For example, in C's standard library you can just do:

open(filename, O_RDWR|O_CREAT, 0666)

but I don't want to resort to using the C function, as it'd be nice to be able to use the functions associated with fstream objects.

(Side Note: there was a question whose title was exactly what I was looking for, but it turned out to be unrelated.)

Upvotes: 9

Views: 20611

Answers (2)

Tom
Tom

Reputation: 2714

In C++17, std::filesystem::permissions was introduced. It will enable you to get and set permissions in a platform-agnostic manner.

Get permissions:

using fs = std::filesystem;
bool owner_can_read =
    fs::status("my_file.txt").permissions() & fs::perms::owner_read != fs::perms::none;

Set permissions (add all permissions for owner and group, that is, add modes 0x770 on unix):

using fs = std::filesystem;
fs::permissions("my_file.txt",
                fs::perms::owner_all | fs::perms::group_all,
                fs::perm_options::add);

Example based on an example from cppreference.

Upvotes: 9

Miles Budnek
Miles Budnek

Reputation: 30569

You cannot. The standard library must be platform agnostic, and permissions like 0600 are meaningless on Windows for example. If you want to use platform-specific features, you'll need to use platform-specific APIs. Of course, you can always call umask() before you open the file, but that's not part of the C++ standard library, it's part of the platform API.

Note: open() isn't part of the C standard library either. It's a platform API. The C standard library function to open a file is fopen().

Upvotes: 8

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