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

29 Aug 2008

      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