From:	Delong <dandelong AT osha DOT igs DOT net>
Newsgroups:	comp.os.msdos.djgpp
Subject:	One of my segments, suddenly not valid?
Date:	Sun, 16 Feb 1997 18:04:15 -0500
Organization:	...
Lines:	57
Message-ID:	<3307926D.E8B@osha.igs.net>
Reply-To:	dandelong AT osha DOT igs DOT net
NNTP-Posting-Host:	ttya13.osha.igs.net
Mime-Version:	1.0
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Sorry about the length of this message ...
I seem to be coming across seg violations when accessing the same memory
that I allocated earlier. By allocating memory I mean creating a new
object (class) that I have declared. 

I made some output routines that wrote the addresses my program was
using for these objects, such as the objects address, the address held
to by its 'char *name' parameter, and the value at this 'name' pointer.
When I accessed the memory at this 'name' pointer (it often happens
during a 'strlen(object->name)' delcaration, but also when I call one of
the objects functions like object->paint()).

The parent object has these 'objects' added to it and it has a list of
pointers, and the value of each object pointer and the pointers (char
*name) within the object are the same as when I allocated the new object
but when I try to access the memory at any pointer in the object (call a
function, access 'char *' member) later on in the program I get a
SIGSEGV error and the usual CPU dump.

I am using this as my startup params:
int _crt0_startup_flags = _CRT0_FLAG_NEARPTR | _CRT0_FLAG_NONMOVE_SBRK;

Is this really a problem with segments somehow becoming invalid without
my deallocating anything? I'd greatly appreciate it if anyone could
offer a suggestion as to what's going on here, I don't have a clue why
the same address produces a segviolation.

Here are the two output files, the first was taken as the objects were
added to the program and the second was taken when they were about to
draw themselves (since the object->paint() function was causing a
segviolation at first).

Output file as list items were created for each directory found
'list.op'
address=0x65880 | name=0x65898 *name=. | cname=ListItem
address=0x65900 | name=0x65918 *name=.. | cname=ListItem
address=0x11dd084 | name=0x11dd09c *name=MAKEPIB | cname=ListItem
address=0x11dd204 | name=0x11dd21c *name=FNT | cname=ListItem
address=0x11dd2c4 | name=0x11dd2dc *name=IMG | cname=ListItem
address=0x11dd344 | name=0x11dd35c *name=MAKEPFN | cname=ListItem
address=0x11dd444 | name=0x11dd45c *name=TEST | cname=ListItem
address=0x11dd5c4 | name=0x11dd5dc *name=PCX2PIB | cname=ListItem

The second output file, the object pointers before painting (the break
at '*name=' is the point at which the segv occurred, before it could
write the value)
'output'
address=0x65880 | name=0x65898 *name=. | cname=ListItem
address=0x65900 | name=0x65918 *name=.. | cname=ListItem
address=0x11dd084 | name=0x11dd09c *name=

Thanks,
-- 
 ... Andrew Delong
______________________________________________________________
Check out my hompage ... Great for graphics & DOS programming
http://www.osha.igs.net/~dandelong/nash.htm

- Raw text -