Message-ID:	<36318BAA.91343991@stargate.net>
From:	John Kissell <jdk AT stargate DOT net>
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Newsgroups:	comp.os.msdos.djgpp
Subject:	Nested structure problem (maybe)?
Lines:	73
Date:	Sat, 24 Oct 1998 01:11:22 -0700
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To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

The following is a snippet from a 'C' file that contains many long and
nested structures. By nested, a main structure 'OBJECT_TYPE *list'
contains pointers to other structures which contain pointers to lesser
structures and so on. It compiles and links with no errors *or warnings*
but I get a SIGSEGV at the 'p=record->text;' line. The rub is that Rhide
in 'run to cursor' and then debug shows that record->text contains a
valid string of type char, and in fact, the correct string in the
correct place for the file that was read in as a test of the code! But
the program when run unhindered under Rhide stops with a SIGSEGV at the
'p = record->text;' line? The nested structures are only four levels
deep at this point so I believe that I've made a mistake somewhere but I
dont have a clue where to begin because the structures work perfectly in
other functions. I can post all the files, but posting a small
compilable portion is impossible. Any ideas out there as to what to look
for? The behavior leads me to believe that there is a a subtle error at
the beginning of the function, but darned if I or the compiler can spot
it!


ps. I typed part of the error codes generated when the program was run
directly from the DOS prompt (from a 'print screen' printout). I would
like to capture them all to include here but I dont know how. :( 

ps2: This was run under DOS 6.2 on a P75.


<snip>


int ParseFile(OBJECT_TYPE *list)
{ char command[6][2] = {"Z","X","K","I","T","G"},
       *p,*p1,*p2,tmp[256],tmp2[256];
  int n,G;
  double CX=0,CY=0,CI=0,CJ=0,X=0,Y=0,I=0,J=0,arc,start,inc,r;
  RECORD_TYPE *record;
  OBJECT_TYPE *graph_win;

  graph_win=TagSearch(list,GRAPH_WIN); /* in debug this points to the
correct data */
  record=graph_win->file->records;     /* this also */ 
  vflag.max=vflag.graph=0;             /* and this */
  view_count=0;                        /* I'll get rid of this global
eventually */ 

  do{
  X=CX; Y=CY;
  vflag.park = 0;                       /* this one too */
  p = record->text; /******* SIGSEGV first flagged here ******/
  p1 = tmp;         /* Run to cursor at the *end* of this line and then
debug in Rhide shows that record->text contains exactly what it is
supposed to?


<snip>



partial error code listing:

Shutting down Allegro
Exiting due to signal SIGSEGV
Page fault at eip=000046b4, error=0004
eax=00000000 ebx=00006bc4 ecx=0000000a edx=0008f0a0 esi=00000054
edi=0004c790
ebp=0008c2dc esp=0008c04a

etc...


ps3: The OBJECT_TYPE structure does contain pointers to ALLEGRO entities
but none are referenced herein. So am I correct in assuming that the
'Shutting down Allegro' message is just a hook into DJ's shutdown
procedure to unload ALLEGRO interrupts?

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