Hello ppl,
Plz direct me to appropriate g++ mailing list if i got it all
wrong.
I've got this small code i made while thinking about c++
exceptions, java exceptions & signals. I am able to throw an exception
from inside a signal handler & its properly caught inside the main catch
block.
However if I remove the sigsetjmp call the thrown exception is
not caught in the main block but lands up with the default handler which
terminates the process.
/* ---------------------------------------------------------------------*/
/* This program only works properly if you call g++ with
the option -fnon-call-exceptions, otherwise it causes
the exception thrown from inside the signal handler not to be caught
& this unhandled exception then makes its way to the default exception
handler which then just aborts & dumps core.
*/
#include <stdexcept>
#include <signal.h>
#include <setjmp.h>
int savesigs;
jmp_buf env;
stack_t ss;
int a; int b; int c;
void sig_handler(int signum, siginfo_t* info, void* arg) {
printf("Inside the signal Handler.\n");
throw "Floating point exception\n";
return; /* Unreachable code. */
}
int main(void) {
struct sigaction act;
act.sa_sigaction = sig_handler;
act.sa_flags = SA_ONSTACK | SA_SIGINFO;
if (sigaction(SIGFPE, &act, NULL) != 0) return -1;
try {
/*remove this sigsetjmp block & the program behaviour changes.why?*/
if (sigsetjmp(env, savesigs) !=0) {
throw "fault thrown in user context(as opposed to signal contxt!";
}
a = 12; b =0;
c = a/b;/* This is to be resumed */
printf("\nThe value of c is: %d", c); /* Wont be called coz of excep */
}
catch(const char* msg) {
printf("\nException caught.");
printf("%s", msg);
printf("\n");
b=2;
/* Resume the exception causing code here. (Is that possible?)
goto restart_point where restart_point is a label inside the try block
would result in a compile error.*/
}
printf("\nThe value of a is: %d", a);
printf("\nThe value of b is: %d", b);
printf("\nThe value of c is: %d", c);
return 0;
}
/*-------------------------------------------------------------------*/
..........Here is the output:
/*-----------------------------------------*/
Inside the signal Handler.
Exception caught.Floating point exception
The value of a is: 12
The value of b is: 2
The value of c is: 0
/*----------------------------*/
........& here is the output with the sigsetjmp call block
entirely commented out.
/*-------------------------------*/
Inside the signal Handler.
Aborted (core dumped)
/*-------------------------*/
I dont have the slightest idea how is this happening.
Can someone plz comment on this.
Thanks,
--
Devrat Mittal
Department of Computer Science,
University of Pune.
M.tech 2nd year
Roll no. 2002301
