When setjmp is called how can the if statement evaluate to true or false
when setjmp only returns 0 or non-zero?
struct pcb {
void *(*start_routin e) (void *);
void *arg;
jmp_buf state;
int stack[1024];
};
struct pcb *pcb_pointer;
pcb_pointer = (struct pcb *) malloc(sizeof(s truct pcb));
if(setjmp(pcb_p ointer->state)) {
current->start_routine( current->arg);
printf("Thread returned\n");
exit(0);
} 20 2321
>When setjmp is called how can the if statement evaluate to true or false when setjmp only returns 0 or non-zero?
There is no true or false in C89. if statements execute the "then" clause
(even though there's no "then" keyword) if the condition evaluates to
non-zero.
While C99 has true and false, this has nothing to do with if statements.
Gordon L. Burditt
In article <d1**********@n ews.net.uni-c.dk>, JS <dsa.@asdf.co m> wrote: When setjmp is called how can the if statement evaluate to true or false when setjmp only returns 0 or non-zero?
Have a coffee, go outside, and sit under a tree (or, if the weather
fails to be cooperative, at least get away from the computer), and
contemplate the difference between true/false and nonzero/zero, and you
will be enlightened.
dave
--
Dave Vandervies dj******@csclub .uwaterloo.caThe Kremlin has a mother these days?
After a fflush(stdin), it might end up having three mothers.
--Joona I Palaste and Gordon Burditt in comp.lang.c
"Dave Vandervies" <dj******@csclu b.uwaterloo.ca> skrev i en meddelelse
news:d1******** **@rumours.uwat erloo.ca... In article <d1**********@n ews.net.uni-c.dk>, JS <dsa.@asdf.co m> wrote:When setjmp is called how can the if statement evaluate to true or false when setjmp only returns 0 or non-zero?
Have a coffee, go outside, and sit under a tree (or, if the weather fails to be cooperative, at least get away from the computer), and contemplate the difference between true/false and nonzero/zero, and you will be enlightened.
Well I have only Java experience and not yet found anything about this
definition in K&R.
"Gordon Burditt" <go****@hammy.b urditt.org> skrev i en meddelelse
news:42******** **************@ news.airnews.ne t... When setjmp is called how can the if statement evaluate to true or false when setjmp only returns 0 or non-zero?
There is no true or false in C89. if statements execute the "then" clause (even though there's no "then" keyword) if the condition evaluates to non-zero.
While C99 has true and false, this has nothing to do with if statements.
Gordon L. Burditt
Where can I find C89 and C99??
JS wrote: When setjmp is called how can the if statement evaluate to true or false when setjmp only returns 0 or non-zero?
Have a coffee, go outside, and sit under a tree (or, if the weather fails to be cooperative, at least get away from the computer), and contemplate the difference between true/false and nonzero/zero, and you will be enlightened.
Well I have only Java experience and not yet found anything about this definition in K&R.
I have found that 0 (zero) and !0 (not zero) work well for false and
true checking.
Mark Odell <od*******@hotm ail.com> writes: I have found that 0 (zero) and !0 (not zero) work well for false and true checking.
I have found that 1 works well as !0.
--
Ben Pfaff
email: bl*@cs.stanford .edu
web: http://benpfaff.org
Ben Pfaff wrote: Mark Odell <od*******@hotm ail.com> writes:
I have found that 0 (zero) and !0 (not zero) work well for false and true checking.
I have found that 1 works well as !0.
Yeah but that breaks my "no numbers except zero" rule. :-) Besides,
sometimes 1 looks like l (ell).
I found this example:
#include <setjmp.h>
#include <stdio.h>
jmp_buf ex;
static int foo (int a, int b)
{
if (!b)
longjmp (ex, 1); /* THROW */
else
return a/b;
}
int main (void)
{
int x = 0, y = 1, z = 0;
if (setjmp (ex) == 0) /* TRY : longjmp branches back to here */
{
x = foo(y, z);
}
else /* CATCH */
{
printf ("Exception: attempt to divide by zero\n");
}
}
When foo is called after setjmp has been called, longjmp is called. Then
control jumps to setjmp but this time setjmp does not return 0 and
therefore: printf ("Exception: attempt to divide by zero\n"); is executed.
But I don't understand why setjmp don't return 0 after the longjmp call. Is
it because the second parameter to longjmp is used as the return value for
setjmp?
Or does the second paramter replace 0 in: if (setjmp (ex) == 0)?
JS wrote: When setjmp is called how can the if statement evaluate to true or false when setjmp only returns 0 or non-zero?
Since false is 0 and true is non-zero, I fail to see your problem. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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