Re: [boost] File operations: Win32 question [was Re: the first version of abstract path...]

From: Chris Little (cslittle_at_[hidden])
Date: 2002-02-23 11:46:31

on 2/23/02 10:31 AM, Beman Dawes at bdawes_at_[hidden] wrote:

> I'm working on more file system functionality (to be packaged with
> Dietmar's directory iterators).
> 
> At 07:48 AM 1/30/2002, Ken Hagan wrote:
> 
>> ... at least in the Windows world, a mounted filesystem will either
>> store names on the disc in "the current code page" (MS-DOS and early
>> Windows) or as "Unicode" (FAT32 and NTFS). For this reason, semi-
>> serious manipulation of files and file systems on NT/2K/XP is done
>> with wchar_t rather than char. The latter is simply blind to a range
>> of names that might exist. (There's another reason too, since the
>> char-based APIs can't handle paths longer than 260 characters, and
>> this limit can be exceeded by UNC-style names.)
> 
> How does this work?  The Win32 API traffics mostly in character strings.
> 
> For example, say we have a function template:
> 
>  template< typename CharT >
>  bool exists( const std::basic_string<CharT> & path );
> 
> The Win32 char implementation might look like this:
> 
>  template<> // specialization for char
>  bool exists<char>( const std::basic_string<char> & path )
>  {
>    return GetFileAttributes( path.c_str() ) != 0xFFFFFFFF;
>  }
> 
> What does the wchar_t implementation look like?  There isn't a
> GetFileAttributes overloaded for wchar_t; GetFileAttributes itself is
> apparently Unicode enabled.  I guess that means the wstring path argument
> has to be converted somehow before calling GetFileAttributes().
> 
> I'd appreciate seeing the preferred code from someone who has actual
> experience with Unicode path names.
> 
> Thanks,
> 
> --Beman
> 

I haven't done much work with this but I can give you the background.

The file apis provide a unicode and non-unicode version.  The function name
is suffixed with W for unicode and A for non-unicode.  The unsuffixed name
is just a define that is set to either the W or A function depending on
whether UNICODE is defined.

I.e. GetFileAttributes is either GetFileAttributesW or GetFileAttributesA.

The A version takes an LPCSTR (const char*) and the W version takes an
LPCWSTR (const wchar_t *)

You can specifically call either version.  On Windows 95/98/Me you need to
add Microsoft's unicode layer to your project to access the W version of the
apis.

As Ken mentioned, the A versions are limited by MAX_PATH but the W versions
are not.

Chris