check if directory is writable in a portable way

[Mark Hammond]

On 28/02/2012 9:07 PM, Andrea Crotti wrote:
> How should I check if I can create files in a directory?

By trying to create them there :)  Presumably you want to know that so 
you can write something "real" - so just write that something real.

The problem gets quite hard when you consider things like elevation - 
your *user* may have rights to write to a directory but only when 
elevated - think writing into Program Files.  Further, this check can 
only ever be transient - what if you have the rights by virtue of a 
group membership, but tomorrow you are no longer in that group?  Or by 
virtue of being the "owner" of the directory but later losing the ownership?

The only reasonable way to check is to write to it, and you may as well 
skip attempting to write a temp file - just write what you care about 
and handle failure in the most graceful way you can.  This is what 
almost every app does - consider apps with a "save as" dialog - they 
never check the directory is writable, they just attempt the actual 
write and handle the failure.

Mark