Re: [boost] [Filesystem] Querying a card reader can throw on Windows

From: Martin Adrian (adrianm_at_[hidden])
Date: 2006-04-14 13:48:13

Angus Leeming <angus.leeming <at> btopenworld.com> writes:

> If I understand correctly, the idiom to check whether a directory exists
> using Boost.Filesystem is
> 
>     if (fs::exists(path) && fs::is_directory(path))
> 
> Under normal conditions the code above shouldn't throw, right?

Welcome to the wonderful world of filesystem exceptions. Your code will throw 
on many conditions. Some I know from the top of my head are (on windows):
1. path is a system file like pagefile.sys
2. the user don't have access to an element in the path.

I have tried to point out several times that filesystem operations can and 
will throw. Production code without try/catch around ALL filesystem operations 
will cause problems (and don't assume that the catch statement should only 
handle racing and filesystem corruption exceptions).

I think the documentation should have big red letters saying:
- Never use any filesystem operation in production code without proper 
try/catch guards (or use the non-throwing versions in 1.34).
- Never assume that an operations "will not throw under normal conditions" 
because it will.

A good way to test your code is to run the application as a non-administrator 
and enter "c:\" and "C:\pagefile.sys" as test paths.