Deniz Dogan writes:
> I have a question regarding the st_mode field of the "stat" struct in
> sys/stat.h. I'd like to know how to use the S_IRWXU, S_IRWXG and
> S_IRWXO flags to mask the mode_t value into human readable form such
> as 755, 644, etc. Currently I do something similar to this:
>
> usr_t = (mod & S_IRWXU);
>
> usr_r = (mod & S_IRUSR);
> usr_w = (mod & S_IWUSR);
> usr_x = (mod & S_IXUSR);
>
> However, this does not produce the required result.

While I have no idea what your 'desired result' is, using
mode & 07777 should mask out all 'non-permission' bits (I do not quite
see the point of replacing 'arcane numbers' with 'cryptic
abbreviations' [which are longer] ...).

On 11 Maj, 13:40, Rainer Weikusat wrote:
> Deniz Dogan writes:
> > I have a question regarding the st_mode field of the "stat" struct in
> > sys/stat.h. I'd like to know how to use the S_IRWXU, S_IRWXG and
> > S_IRWXO flags to mask the mode_t value into human readable form such
> > as 755, 644, etc. Currently I do something similar to this:
>
> > usr_t = (mod & S_IRWXU);
>
> > usr_r = (mod & S_IRUSR);
> > usr_w = (mod & S_IWUSR);
> > usr_x = (mod & S_IXUSR);
>
> > However, this does not produce the required result.
>
> While I have no idea what your 'desired result' is, using
> mode & 07777 should mask out all 'non-permission' bits (I do not quite
> see the point of replacing 'arcane numbers' with 'cryptic
> abbreviations' [which are longer] ...).

My desired output is that given a mode_t representing a 755 file,
usr_t is 7 and usr_r, usr_w and usr_x are all 1.

Deniz Dogan wrote:
> On 11 Maj, 13:40, Rainer Weikusat wrote:
> > Deniz Dogan writes:
> > > I have a question regarding the st_mode field of the "stat" struct in
> > > sys/stat.h. I'd like to know how to use the S_IRWXU, S_IRWXG and
> > > S_IRWXO flags to mask the mode_t value into human readable form such
> > > as 755, 644, etc. Currently I do something similar to this:
> >
> > > usr_t = (mod & S_IRWXU);
> >
> > > usr_r = (mod & S_IRUSR);
> > > usr_w = (mod & S_IWUSR);
> > > usr_x = (mod & S_IXUSR);
> >
> > > However, this does not produce the required result.
> >
> > While I have no idea what your 'desired result' is, using
> > mode & 07777 should mask out all 'non-permission' bits (I do not quite
> > see the point of replacing 'arcane numbers' with 'cryptic
> > abbreviations' [which are longer] ...).

> My desired output is that given a mode_t representing a 755 file,
> usr_t is 7 and usr_r, usr_w and usr_x are all 1.

You're already near to the solution. If you follow Rainers
advice you would do

usr_t = ( mod & 0700 ) >> 6;

usr_r = ( mod & 0400 ) >> 8;
usr_w = ( mod & 0200 ) >> 7;
usr_x = ( mod & 0100 ) >> 6;

I am not totally convinced that this is the "best" way since
it assumes that you know how the bits in the value of st_mode
as returned by stat() encode the permission settings. While
it will probably work the way Rainer writes on most systems,
I am not 100% sure that it has to work on all systems, so I
personally would prefer (I am also not a big fan of "magic"
numbers in programs):

usr_r = ( mod & S_IRUSR ) ? 1 : 0;
usr_w = ( mod & S_IWUSR ) ? 1 : 0;
usr_x = ( mod & S_IXUSR ) ? 1 : 0;

usr_t = ( usr_r << 2 ) | ( usr_w << 1 ) | usr_x;

The bits for the group and others can be treated in exactly
the same way.
Regards, Jens
--
\ Jens Thoms Toerring ___ jt@toerring.de
\__________________________ http://toerring.de

On 11 Maj, 13:56, j...@toerring.de (Jens Thoms Toerring) wrote:
> Deniz Dogan wrote:
> > On 11 Maj, 13:40, Rainer Weikusat wrote:
> > > Deniz Dogan writes:
> > > > I have a question regarding the st_mode field of the "stat" struct in
> > > > sys/stat.h. I'd like to know how to use the S_IRWXU, S_IRWXG and
> > > > S_IRWXO flags to mask the mode_t value into human readable form such
> > > > as 755, 644, etc. Currently I do something similar to this:
>
> > > > usr_t = (mod & S_IRWXU);
>
> > > > usr_r = (mod & S_IRUSR);
> > > > usr_w = (mod & S_IWUSR);
> > > > usr_x = (mod & S_IXUSR);
>
> > > > However, this does not produce the required result.
>
> > > While I have no idea what your 'desired result' is, using
> > > mode & 07777 should mask out all 'non-permission' bits (I do not quite
> > > see the point of replacing 'arcane numbers' with 'cryptic
> > > abbreviations' [which are longer] ...).
> > My desired output is that given a mode_t representing a 755 file,
> > usr_t is 7 and usr_r, usr_w and usr_x are all 1.
>
> You're already near to the solution. If you follow Rainers
> advice you would do
>
> usr_t = ( mod & 0700 ) >> 6;
>
> usr_r = ( mod & 0400 ) >> 8;
> usr_w = ( mod & 0200 ) >> 7;
> usr_x = ( mod & 0100 ) >> 6;
>
> I am not totally convinced that this is the "best" way since
> it assumes that you know how the bits in the value of st_mode
> as returned by stat() encode the permission settings. While
> it will probably work the way Rainer writes on most systems,
> I am not 100% sure that it has to work on all systems, so I
> personally would prefer (I am also not a big fan of "magic"
> numbers in programs):
>
> usr_r = ( mod & S_IRUSR ) ? 1 : 0;
> usr_w = ( mod & S_IWUSR ) ? 1 : 0;
> usr_x = ( mod & S_IXUSR ) ? 1 : 0;
>
> usr_t = ( usr_r << 2 ) | ( usr_w << 1 ) | usr_x;
>
> The bits for the group and others can be treated in exactly
> the same way.
> Regards, Jens
> --
> \ Jens Thoms Toerring ___ j...@toerring.de
> \__________________________ http://toerring.de

Thanks alot for your help!