Re: [Boost-users] [filesystem] Catching permissions errors?

From: Allen Cronce (allenslists_at_[hidden])
Date: 2008-08-28 21:38:26

In case anyone is interested...

Turns out that my original code intended to detect permissions errors  
in a cross platform way did not work on Windows. The comparison has to  
be performed on the exception's error_code, not the error_code's  
value. The value seems to be platform specific.

So the correct (I think) cross platform solution for detecting a  
permissions error is as follows:

        if (boost::system::posix_error::permission_denied == e.code())
        {
                std::cout << "The error code indicates a permissions error, as  
expected. " << std::endl;
        }

Note the absence of the ".value()" in the comparison.

Best,
--
Allen Cronce
On Aug 10, 2008, at 9:31 AM, Allen Cronce wrote:
> Hi all,
>
> I need to programmatically test for permissions errors during path  
> iteration. I think what I need to do is catch the filesystem  
> exception, then drill out the error code and compare it to the  
> permission_denied error value.
>
> Here's a code fragment written under boost 1.35 that demonstrates  
> what I'm talking about:
>
> 	try
> 	{
> 		// Force a permissions error on *nix machines when not running as  
> root.
> 		// Note that this code is is for demonstration purposes only.  
> Assume that
> 		// in the real implementation I'm doing something else here with the
> 		// filesystem that *might* throw a permissions error.
> 		boost::filesystem::path testDirPath( "/usr/local/cant_touch_this" );
> 		create_directory(testDirPath);
> 	}
> 	catch(const boost::filesystem::filesystem_error& e)
> 	{
> 		// Check the error code to see if it's a permissions error
> 		if (boost::system::posix_error::permission_denied ==  
> e.code().value())
> 		{
> 			std::cout << "The error code indicates a permissions error, as  
> expected. " << std::endl;
> 		}
> 		else
> 		{
> 			std::cout << "Hmm... I didn't get a permissions error. That's  
> wrong." << std::endl;
> 		}
> 	}
>
> Is this basically the right approach?
>
> Note that one concern I have is maintainability. A coworker wrote  
> similar code to the above, but under boost 1.33.1. That code broke  
> under 1.35 due to significant changes to the filesystem exceptions  
> mechanism.
>
> I understand that there are no guarantees moving forward to new  
> boost versions. I knew the job was dangerous when I took it ;-)  But  
> if there's anything I can do today to future-proof a little bit,  
> that would be great.
>
> Thanks in advance for any feedback or suggestions.
>
> Best,
> --
> Allen Cronce