Re: [boost] filesystem exists/is_directory suggestion

From: Beman Dawes (bdawes_at_[hidden])
Date: 2004-09-09 14:32:28

At 05:12 AM 9/9/2004, Martin wrote:

 >The filesystem status operations exists & is_directory will both throw if 

 >the status of the file can't be determined (access problems or race
 >conditions).

CVS for exists() was changed in March to always determine existence or no, 
and not to throw.

 >I think this makes the operations overly complicated to use since you 
need
 >to enclose them in try catch blocks. You normally guard operations that
 >use files in some way but it is easy to forget try/catch around exists /
 >is_directory.

That isn't at all clear to me. I've rarely if ever seen people put 
try/catch around is_directory(). The thinking is that throws from 
is_directory all represent real errors, so should be caught higher up in 
the call tree along with all other general filesystem errors.

 >
 >(Noticed that exists has been updated in CVS to return true on error 
which
 >is
 >probably ok but I think is_directory need to be updated as well.)
 >
 >I think a good solution would be to have a non-throwing overload where 
the
 >return value in case of error is specified.
 >
 >bool is_directory(const tdFS::path& aPath, bool aErrorRet) {
 >  try { return tdFS::is_directory(aPath); } catch (...) { return 
aErrorRet;
 >}
 >}
 >
 >Another way could be to have a "is_accessable" operation that determines 
if
 >the status of the entry can be determined but it will not solve the 
racing
 >problem.

Yes, is_accessable() might be useful. But the use cases I can think of are 
a bit theoretical. Anyone else have an opinion? I think I'd like to hear 
about so real-life needs (rather than theoretical or hypothetical needs) 
before deciding.

Thanks,

--Beman