Re: [boost] [filesystem] temp_dir_path()

Subject: Re: [boost] [filesystem] temp_dir_path()
From: Jeff Flinn (TriumphSprint2000_at_[hidden])
Date: 2010-10-09 14:19:35

PB wrote:
> On Sat, Oct 9, 2010 at 5:36 PM, Jeff Flinn
> <TriumphSprint2000_at_[hidden]> wrote:
>> The need for portably obtaining 'the' temporary-directory-path has been
>> brought up a few times(but never addressed AFAICT), and I am now in the need
>> for this as well.
>>
>> Windows has the GetTempPath, which follows a specific order of looking for a
>> temporary directory path. If GetTempPath returns 0, GetLastError provides a
>> system error.
>>
>> Posix relies on getEnv("TMPDIR"), which returns 0 if the environment
>> variable does not exist.
>>
>> The following windows and posix implementation would be in the detail
>> namespace:
>>
>>  BOOST_FILESYSTEM_DECL
>>  path temp_dir_path(system::error_code* ec)
>>  {
>> #   ifdef BOOST_POSIX_API
>>      const char* val = getenv("TMPDIR");
>>      return val? path(val) : path();
>>
>> #   else  // Windows
>>
>>      std::vector<Path::value_type> buf(GetTempPathW(0, NULL));
>>
>>      if(GetTempPathW(buf.size(), &buf[0]))
>>          return path(buf.begin(), buf.end());
>>
>>      int errval(::GetLastError());
>>      if (ec)
>>          ec->assign(errval, system_category());
>>
>>      return path()
>> #   endif
>>  }
>>
>> Questions:
>> - should Posix return an empty path or an error when empty?
>> - should Windows provide a more 'temp-path' centric error?
>> - should both verify the path exists?
>> - if the path does not exist should one be created?
>>
> 
> Jeff,
> 
> A temporary directory getter withing Boost.Filesystem would be a "nice
> to have". In my application, I created a function called
> GetValidatedTempDir() which does the get and validate, so my
> suggestions/comments would be as follows:
> 
> - both flavours should verify the path exists.
> - a more 'temp-path' centric error might be good. I must confess to
> not knowing a great feal about the error codes. I usually have an
> outer catch for const std::exception& and expect that calling what()
> on that would give me something meaningful. If the temporary directory
> getter threw an exception if validation fails, and if calling what()
> on that gave me some idea about a problem with the temp path, then I'd
> be happy.
> - I don't think the path should be created.

Ok, the following uses filesystem's error facility to optionally throw 
or set errcode. It verfies the path is a directory, which IIUC, implies 
path existence.

   path temp_dir_path(system::error_code* ec)
   {
#   ifdef BOOST_POSIX_API
       const char* val = getenv("TMPDIR");

       if (error(val==0,
         ec, "boost::filesystem::temp_dir_path"))
           return path();

       path p(val);

       if (error(!fs::is_directory(p, ec),
         ec, "boost::filesystem::temp_dir_path"))
           return path();

       return p;

#   else  // Windows

       std::vector<Path::value_type> buf(GetTempPathW(0, NULL));

       if (error(GetTempPathW(buf.size(), &buf[0])==0,
         ec, "boost::filesystem::temp_dir_path"))
           return path();

       path p(buf.begin(), buf.end());

       if (error(!fs::is_directory(p, ec),
         ec, "boost::filesystem::temp_dir_path"))
           return path();

       return p;
#   endif
   }

Jeff