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From: ark@alice.UUCP (Andrew Koenig)
Newsgroups: net.unix-wizards
Subject: Steve Rosen's setjmp problem
Message-ID: <3826@alice.UUCP>
Date: Fri, 7-Jun-85 00:20:16 EDT
Article-I.D.: alice.3826
Posted: Fri Jun  7 00:20:16 1985
Date-Received: Fri, 7-Jun-85 05:23:02 EDT
Organization: Bell Labs, Murray Hill
Lines: 30

Steve Rosen complains that the following C program fails:

#include <setjmp.h>

static jmp_buf env;
int mode;

main(){
	foo();
	longjmp(env, 1);
}

foo(){

  mode = setjmp(env);
  if (mode != 0) magic();
}

magic()
{
	printf("HERE I AM\n");
	exit(0);
}

The reason the program fails is that foo returns after calling
setjmp.  This destroys the environment that setjmp saved,
so there is nothing for longjmp to return to.  General rule:
every call to longjmp must be made from a function that
is a dynamic descendent of the one that made the corresponding
call to setjmp.