FDI: Constify some variables

[Andrew Talbot]

James Hawkins wrote:

> That's not how it works.  PFNOPEN, et al., has a specific definition
> that is similar to, but not the same as, the corresponding low-level
> file IO function.  If you make a change to a public header, you need
> to check the same header in the SDK and make sure that the change is
> warranted.  As it stands, this is wrong.
> 

Hi James,

I accept your point, so the following is not an argument, but just for
interest's sake I am posting this quote from "Microsoft FCI/FDI Library
Description":

"The pfnopen, pfnread, pfnwrite, pfnclose, and pfnseek parameters should
point to functions which perform file open, file read, file write, file
close, and file seek operations respectively.  These functions should
accept parameters identical to those for the standard _open, _read, _write,
_close, and _lseek functions, and should likewise have identical return
codes."

I looked at the two function prototypes that I reviewed for these standard
functions in our include/msvcrt/io.h and noted that they are constified.

But yes, I shall check the public header, in future.

Thanks,

-- Andy.