stat() problems.

stat() problems.

[Stefanos Koutsoutos]

Hi,

I'm facing problems with stat() system call. It seems that it follows
filesystem links! To be more accurate I try:

struct stat buf;
stat("this_is_a_link", &buf);

and then:	S_ISLNK( buf.st_mode )  is false!

More, the mode is the same as the mode of the file it links to! I think
that this is not what it supposed to be done by stat(). Any ideas??

Thanks in advance.
Stefanos.

-- 
____________________
Stefanos Koutsoutos
Developer
MD5 S.A.
koutsoutos@md5sa.com
www.md5sa.com

Re: stat() problems.

[Alexandre P. Nunes]

Stefanos Koutsoutos wrote:

>Hi,
>
>I'm facing problems with stat() system call. It seems that it follows
>filesystem links! To be more accurate I try:
>
>struct stat buf;
>stat("this_is_a_link", &buf);
>
>and then:	S_ISLNK( buf.st_mode )  is false!
>
>More, the mode is the same as the mode of the file it links to! I think
>that this is not what it supposed to be done by stat(). Any ideas??
>
>Thanks in advance.
>Stefanos.
>
>  
>

stat() follows symlinks. That's why there's lstat(), try it instead.

Cheers,

Alexandre

Re: stat() problems.

[Stefanos Koutsoutos]

Thanks a lot Alexandre!


On Thu, 2002-08-01 at 14:48, Alexandre P. Nunes wrote:
>
> stat() follows symlinks. That's why there's lstat(), try it instead.
> 
> Cheers,
> 
> 

-- 
____________________
Stefanos Koutsoutos
Developer
MD5 S.A.
koutsoutos@md5sa.com
www.md5sa.com

C Language Reference for @ and :

[Nate]

I am looking at some C code and I cannot find any language reference as to
what the '@' symbol or token means...

For, example, from the header file I am trying to interpret....

/////////////////////////////////////////////////////////////////
static unsigned char P1 @ 0x90;
static unsigned char P2 @ 0xA0;
static unsigned char P3 @ 0xB0;
/////////////////////////////////////////////////////////////////



Also what does these colons mean... ( I understand this is creating a new
type and it is a "public by default" class for a bit watching type.)  But
what does the colon do?  Initialize defualts?

/////////////////////////////////////////////////////////////////
typedef struct
{
   unsigned B0:1;
   unsigned B1:1;
   unsigned B2:1;
   unsigned B3:1;
   unsigned B4:1;
   unsigned B5:1;
   unsigned B6:1;
   unsigned B7:1;
} SFR;
/////////////////////////////////////////////////////////////////


Thanks,

Nate

Re: C Language Reference for @ and :

[Stephen Satchell]

At 01:50 PM 8/28/02 -0700, Nate wrote:
>I am looking at some C code and I cannot find any language reference as to
>what the '@' symbol or token means...
>
>For, example, from the header file I am trying to interpret....
>
>/////////////////////////////////////////////////////////////////
>static unsigned char P1 @ 0x90;
>static unsigned char P2 @ 0xA0;
>static unsigned char P3 @ 0xB0;
>/////////////////////////////////////////////////////////////////

The compiler implements an extension that indicates that the unsigned char 
P1 is at the absolute address 0x00000090, and when the compiler generates 
an access it should use this absolute address.  The equivalent ANSI C code 
using pointer variables might be:

static unsigned char * const P1 = (unsigned char *) 0x90;
static unsigned char * const P2 = (unsigned char *) 0xA0;
static unsigned char * const P3 = (unsigned char *) 0xB0;

Or the other way to do this is to use the preprocessor:

#define P1 ((unsigned char *)(0x90));
#define P2 ((unsigned char *)(0xA0));
#define P3 ((unsigned char *)(0xB0));

I used to see this with some compilers for machines that had memory-mapped 
I/O in which the registers were at hardware-fixed locations.  This is 
actually bad form, particularly when a driver can be used with multiple 
devices and there was no way to "map in" the particular device interface.

This is an oldie, and VERY machine-dependent.

>Also what does these colons mean... ( I understand this is creating a new
>type and it is a "public by default" class for a bit watching type.)  But
>what does the colon do?  Initialize defualts?
>
>/////////////////////////////////////////////////////////////////
>typedef struct
>{
>    unsigned B0:1;
>    unsigned B1:1;
>    unsigned B2:1;
>    unsigned B3:1;
>    unsigned B4:1;
>    unsigned B5:1;
>    unsigned B6:1;
>    unsigned B7:1;
>} SFR;
>/////////////////////////////////////////////////////////////////

Bitfield definition.  Page 136-138 in the first edition of K&R _The C 
Programming Language_, 149-150 in the second edition.  This is part of ANSI 
C, but the implementation definition makes it a non-portable 
construct.  Some people like to try to use bitfields in networking, with 
disastrous results as you change compilers or even versions of the same 
compiler.

The colon introduces a bit-width.  In your definition, you are defining 
seven bits in the variable SFR to be one-bit values that can be set or 
reset using a simple assignment statement:

      SFR.B0 = 1;   /* Set a single bit */
      SFR.B4 = 0;   /* Reset a single bit */

The problem is that which structure variables get assigned to which bits is 
not specified in the standard, but is labelled "implementation 
defined."  From the definition you show, I suspect that the compiler 
originally used to compile the code assigned bit fields from the low-order 
bits to the high-order bits of a regular integer.  Other compilers may 
start from the most significant bit and work down, which is why this 
construct is highly non-portable if you store or read the variable to/from 
storage or a network.

Satch

Stack and Heap

[Nate]

Are there any commands / functions to call to find out memory info?

For example, if I am writing a program that is using a ton of memory.
Everything is working and then I add more code needing more memory but it
crashes and I think I may be trying to use too much...  Can I call some
commands to see how much memory is left?  And/Or how much I am using?  For
Stack and Heap?


Thank You,

Nate

Re: C Language Reference for @ and :

[Nate]

I thought that could be the answer on the bit width issue...

I do not know which compiler was being used but I bet you're right because
this code was to compile for a micro-controller.  So the output was probably
hex code to download onto the chip.  They were probably addresses.

Thank You,

Nate



----- Original Message -----
From: "<Iliyan Malchev>" <ibm@asu.edu>
To: "Nate" <nate@uniwest.com>
Sent: Wednesday, August 28, 2002 2:00 PM
Subject: Re: C Language Reference for @ and :


>
> >
> > I am looking at some C code and I cannot find any language reference as
to
> > what the '@' symbol or token means...
> >
> > For, example, from the header file I am trying to interpret....
> >
> > /////////////////////////////////////////////////////////////////
> > static unsigned char P1 @ 0x90;
> > static unsigned char P2 @ 0xA0;
> > static unsigned char P3 @ 0xB0;
> > /////////////////////////////////////////////////////////////////
> >
>
> The '@' symbol is not standard notation: perhaps the compiler
> you are using has a language extension of some sort.
>
> > /////////////////////////////////////////////////////////////////
> > typedef struct
> > {
> >    unsigned B0:1;
> >    unsigned B1:1;
> >    unsigned B2:1;
> >    unsigned B3:1;
> >    unsigned B4:1;
> >    unsigned B5:1;
> >    unsigned B6:1;
> >    unsigned B7:1;
> > } SFR;
> > /////////////////////////////////////////////////////////////////
>
> The colon defines the width of the respective field in a number of bits
(that
> is, it defined a bit field).  In the example above, you have a structure
where
> each member is one-bit-wide, and the total structure is 8 bits (one
> byte).  Thus if you had the following code:
>
> static SFR val; /* set the structure to all zeroes */
>
> ....
>
> val.B5 = 1; /* set the 5th bit */
> fprintf (stdout, "val: %x\n", (unsigned char)val);
>
> will print out the value
>
> val: 20
>
> (binary 0010 0000, the fifth bit was set).
>
>
>