CHAPTER 68. WINDOWS NT CHAPTER 68. WINDOWS NT
If thefilterpointer is NULL, thehandler pointer is the pointer to thefinallycode block.
During execution, theprevious try levelvalue in the stack changes, so_except_handler3can get information about
the current level of nestedness, in order to know whichscope tableentry to use.
SEH3: one try/except block example
#include <stdio.h>
#include <windows.h>
#include <excpt.h>
int main()
{
int p = NULL;
__try
{
printf("hello #1!\n");
p = 13; // causes an access violation exception;
printf("hello #2!\n");
}
__except(GetExceptionCode()==EXCEPTION_ACCESS_VIOLATION?
EXCEPTION_EXECUTE_HANDLER : EXCEPTION_CONTINUE_SEARCH)
{
printf("access violation, can't recover\n");
}
}
Listing 68.6: MSVC 2003$SG74605 DB 'hello #1!', 0aH, 00H
$SG74606 DB 'hello #2!', 0aH, 00H
$SG74608 DB 'access violation, can''t recover', 0aH, 00H
_DATA ENDS
; scope table:
CONST SEGMENT
$T74622 DD 0ffffffffH ; previous try level
DD FLAT:$L74617 ; filter
DD FLAT:$L74618 ; handler
CONST ENDS
_TEXT SEGMENT
$T74621 = -32 ; size = 4
_p$ = -28 ; size = 4
$SEHRec$ = -24 ; size = 24
_main PROC NEAR
push ebp
mov ebp, esp
push -1 ; previous try level
push OFFSET FLAT:$T74622 ; scope table
push OFFSET FLAT:__except_handler3 ; handler
mov eax, DWORD PTR fs:except_list
push eax ; prev
mov DWORD PTR fs:except_list, esp
add esp, -16
; 3 registers to be saved:
push ebx
push esi
push edi
mov DWORD PTR __$SEHRec$[ebp], esp
mov DWORD PTR _p$[ebp], 0
mov DWORD PTR $SEHRec$[ebp+20], 0 ; previous try level
push OFFSET FLAT:$SG74605 ; 'hello #1!'
call _printf
add esp, 4
mov eax, DWORD PTR _p$[ebp]
mov DWORD PTR [eax], 13
push OFFSET FLAT:$SG74606 ; 'hello #2!'