From mboxrd@z Thu Jan  1 00:00:00 1970
From: Greg Rigole <grigole@rci.rogers.com>
To: "'gcc@gcc.gnu.org'" <gcc@gcc.gnu.org>
Subject: RE: stat problem ?
Date: Fri, 31 Mar 2000 12:49:00 -0000
Message-id: <59C8A3391243D311B5390000E865F4C501CF3B0F@rssesnexb.rogers.com>
X-SW-Source: 2000-03/msg00858.html

The function stat is defined in the manual (in my case, AIX 4.2.1) as
follows:

	int stat (Path, Buffer)
	const char *Path;
	struct stat *Buffer;

The stat function takes a pointer to an ALREADY EXISTING BUFFER. It does not
allocate the buffer for you.

In program #1, you passed an UNITIALIZED POINTER (probably garbage) instead
of one pointing to a buffer large enough for a struct stat. The stat
function blindly attempts to write using the pointer, which probably points
at inaccessible memory. Hence the exception.

In program two, you pass a pointer to a buffer assigned to its own valid
memory, large enough to hold a struct stat. The stat function now correctly
puts the info for the file into that buffer.

A third alternative is:

main(void) {

DIR *dp;
struct dirent *ep;
struct stat *st;
int rc;

dp = opendir ("./");
if (dp != NULL)
{

st=malloc( sizeof( struct stat ) );
if (st == NULL) {
	puts ("Out of memory.");
	exit(-1);
}

while (ep = readdir (dp)) 
{
	
rc=stat (ep->d_name,st);

if (S_ISDIR(st->st_mode)!=0)
	puts (ep->d_name);
else
	{
	printf ("Not a directory : ");
	puts(ep->d_name);
	printf("\n");
	}
}

free( st );

(void) closedir (dp);
}
else
puts ("Couldn't open the directory.");
return;
}
}

In this case, there is extra work involved for a situation where only one
buffer is needed for the entire program lifetime, an ideal situation for a
static (or in this case automatic) buffer.

-----------------------------------------------------------------
PS: Is this group the place for this kind of question? I don't know, I'm
just asking.
-----------------------------------------------------------------

Greg

-----Original Message-----
From: Borsos Zoltán [ mailto:zoltan.borsos@sysdata.siemens.hu ]
Sent: Thursday, March 30, 2000 1:31 AM
To: 'gcc@gcc.gnu.org'
Subject: stat problem ?


Hi everybody !

I'm new in this list and in C too.
I have written a small program that in one version dosen't work
but in the other does it. I'd like to ask the experts explain me the
difference between the programs.

I can compile both free from errors but when I let it run this version
give me the following message :

[main] D:\KOZOS\progik\c\exe\dirsiz_1.exe 1000 (0) handle_exceptions:
Exception:
 STATUS_ACCESS_VIOLATION
[main] dirsiz_1 1000 (0) handle_exceptions: Dumping stack trace to
dirsiz_1.exe.
core

// dirsiz_1.c

#include <dirent.h>
#include <sys/stat.h>
 

main(void) {

DIR *dp;
struct dirent *ep;
struct stat *st;
int rc;

dp = opendir ("./");
if (dp != NULL)
{
while (ep = readdir (dp)) 
{
rc=stat (ep->d_name,st);
if (S_ISDIR(st->st_mode)!=0)
	puts (ep->d_name);
else
	{
	printf ("Not a directory : ");
	puts(ep->d_name);
	printf("\n");
	}
}
(void) closedir (dp);
}
else
puts ("Couldn't open the directory.");
return;
}

-------------------------------------------------

This version works fine :

// dirsiz_2.c

#include <dirent.h>
#include <sys/stat.h>
 

main(void) {

DIR *dp;
struct dirent *ep;
struct stat st;
int rc;

dp = opendir ("./");
if (dp != NULL)
{
while (ep = readdir (dp)) 
{
rc=stat (ep->d_name,&st);
if (S_ISDIR(st.st_mode)!=0)
	puts (ep->d_name);
else
	{
	printf ("Not a directory : ");
	puts(ep->d_name);
	printf("\n");
	}
}
(void) closedir (dp);
}
else
puts ("Couldn't open the directory.");
return;
}

Thanks for the answers !
The answers please to my own address too.

Szambi