Re: [boost] Re: IOStream mmap too restrictive?

From: Jonathan Graehl (jonathan_at_[hidden])
Date: 2004-09-02 16:50:42

>For portability it's best to stick to the win32 API.
>

Sorry ... I didn't realize that was VC++ only.  It looks like the Win32 
API call to set a file's length directly (without writing out bytes to a 
newly created file) is:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/fileio/base/setfilevaliddata.asp

*BOOL* *SetFileValidData(*
  *HANDLE* /hFile/*,
*  *LONGLONG* /ValidDataLength/*
**);
*

In any case it looks like this SetFileValidData for win32, and ftruncate 
for POSIX, could be used by memmap.c to support automatic creation of an 
appropriately sized backing file in the constructor for mapped_file (and 
the constructor for mapped output files in the IO lib could expose 
this).  I still think a truncate/SetFileValidData wrapper would be nice 
for the filesystem lib.

I'm willing to code this if people think it's a good idea.  It frees 
users from having to first create an empty file of the right length first.