[Mingw-users] Temporary File Woes

[MARSHALL K. <Kei...@to...>]

Hi Guys,

I just had an application throw an unexpected "Permission denied"
exception, when it tried to redirect stdout to a named temporary file,
with the file name generated by "tmpnam()".

The problem here lies with the definition of "_P_tmpdir" in stdio.h;
the MinGW implementation has

        #define _P_tmpdir       "\\"

and "tmpnam( mytmpfile )" prepends exactly this pathname prefix
to the proposed file name returned in "mytmpfile"; i.e. the named
temporary file would be created in the root directory of the
*current drive*.

This would be fine, if we could always *guarantee* to have write
permission in the root directory of every drive, which could possibly
host the current working directory!  However, what happens when
PWD refers to a mapped drive on a network share, where we do not
have write permission in the root directory?  Answer: the application
throws the "Permission denied" exception, when it calls "creat()" to
initialise the temporary file stream!  (Yes, my application failed
because PWD referred to just such a network share; and, yes, it
works fine when PWD refers to a local drive, where I *do* have
root directory write permission).

This is quite clearly a bug, arising from an inappropriate definition of
"_P_tmpdir" in stdio.h;  however, is it a MinGW bug, or is it yet another
MS cock up, that allows "tmpnam()" to use this inappropriate definition?

Regards,
Keith Marshall