Thread: understanding setJmp

Hello,

I am trying to implement setjmp for functions.

Code:

#include <setjmp.h>
#include <stdio.h>

jmp_buf arr[3];

void DISP(int x , int i)
{

	if(!setjmp(arr[i]) ) { printf("FUNC SAVED!\n"); return; }
	printf("Func Continues here for buf : %d\n", i);
	printf(" x :%d at buf : %d\n", x , i);

}

int main(void)
{
	int  value;
	int rerun = 0;
	if(!rerun)
	{
		value = 3;
		DISP(0, 0);
	}
	if(!rerun)
	{
		value = 2;
		DISP(1, 1);
	}
	if(!rerun)
	{
		value = 1;
		DISP(2, 2);
	}
	rerun = 1;
	longjmp(arr[0], 1);
}

Does setjmp not save any of the parameter information?

Also, I found this article on setjmp implemented coroutines, it seems you need to allocated memory via an array :
http://fanf.livejournal.com/105413.html

Code:

 void *cogo(jmp_buf here, void (*fun)(void*), void *arg) {
        if (tos == NULL) tos = (char*)&arg;
        tos += STACKDIR STACKSIZE;
        char n[STACKDIR (tos - (char*)&arg)];
        coarg = n; // ensure optimizer keeps n
        if (setjmp(here)) return(coarg);
	fun(arg);
	abort();
    }

Could I possibly use malloc to allocate memory for the stack too?

thank you!

Once you've returned from the function that calls setjmp(), you can no longer jump to it; setjmp() relies on you to keep the function alive for a call from longjmp(). In a sense, setjmp() just creates a pointer to the current stack state, so if you invalidate that, you invalidate the value of the jmp_buf.