Re: [boost] [filesystem] relative_to

From: Beman Dawes (bdawes_at_[hidden])
Date: 2004-03-19 13:20:40

At 02:23 AM 3/13/2004, John Torjo wrote:

 >Dear boosters,
 >
 >I noticed that currently there's no way to get the relative path of path
 >A related to path B.
 >What I mean is, given two **complete** paths, to get the relative path
 >of one related to the other.
 >
 >To give a real example, I have an application that starts in directory
 >initial_path().
 >I have several dialogs that allow the user to browse for files. My
 >requirement is, after the user browses for a file, to  internally ALWAYS
 >store the path relative to initial_path().
 >
 >Since there's no way to do this currently, I created my own function.
 >Do you think it could be a useful addition to filesystem library?

It might be useful, but the problem is one of expectations. The function 
you provided operates only on the lexical path representation; that's OK if 
that is what is expected but could be a pretty rude shock to a programmer 
not expecting that behavior.

For example, relative_to( "c:/foo", "C:/foo" ) returns "c:/foo", which is 
probably not what was desired.

I'm definitely worried that relative_to() as proposed would come to be 
viewed as fragile.

This is similar to the path equality issue. We are dealing with that by 
introducing class path relational operators, working at a lexical level, 
and a function equivalent() which actually performs filesystem operations 
to determine if two paths refer to the same underlying object.

What do others think?

--Beman