«

Hi everybody

i'm playing round with more child process code.

this is a program straight from my textbook:

void main(argv, argc)
int argc; char *argv[];
{
int wch, wpar;

if(!fork())
{
printf("child pid %d\n", getpid());
printf("enter child exit status:");
scanf("%d", &wch);
printf("child exiting\n");
_exit(wch);
}
printf("waiting for child to exit\n");
waitpid(-1, &wpar, 0);
printf("child exit status was %d\n", (wpar>>&0xff);
}


i'm confused, because when i run it i get

child pid 9567
enter child exit status:waiting for child to exit

and the program just hangs without giving me a chance to enter an exit
status for the child.

can anyone explain? thanks.

On 28 Jan 2009 at 23:17, Mike wrote:
> i'm confused, because when i run it i get
>
> child pid 9567
> enter child exit status:waiting for child to exit
>
> and the program just hangs without giving me a chance to enter an exit
> status for the child.

All that's happening is that after the fork(), the child process happens
to be the first to execute: it displays its prompt and blocks at the
scanf() call.

Meanwhile, the parent gets scheduled; it prints its message which gets
appended to your prompt.

You should still be able to enter an exit status - just type one in and
press return!

Mike wrote:
> Hi everybody
>
> i'm playing round with more child process code.
>
> this is a program straight from my textbook:
>
> void main(argv, argc)
> int argc; char *argv[];

I'm starting to think you're taking the ****.

If you are serious, post to comp.unix.programmer. You are learning Unix
system programming, not C.

--
Ian Collins

Mike <> writes:
> i'm playing round with more child process code.
[...]
> can anyone explain? thanks.

Why do you persist in posting to the wrong newsgroup?

Standard C doesn't support processes. Ask your questions in
comp.unix.programmer.

--
Keith Thompson (The_Other_Keith) kst- <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

Mike <> writes:
> i'm playing round with more child process code.
>
> this is a program straight from my textbook:
>
> void main(argv, argc)
> int argc; char *argv[];
> {
[...]

What textbook are you using? The use of the old-style function
definition is excusable if it's a very old book; in that case, you
should get a newer one if at all possible. But the use of void as the
return type of main, though it's a common error, is harder to
understand. The "void" keyword was introduced in the 1989 ANSI C
standard -- the very same document that established the requirement
that main returns int. "void main" has *never* been correct.

(Quibble: an implementation is allowed to accept forms of main other
than the two presented in the standard -- but no implementation is
required to do so, and *all* hosted implementations must support "int
main(void)" and "int main(int argc, char *argv[])".)

--
Keith Thompson (The_Other_Keith) kst- <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

Mike wrote:

> Hi everybody
>
> i'm playing round with more child process code.

This is one too many. You're either trolling, or unable to read and
comprehend. Either way, a waste of time.

You know, you hate it, but:

*plonk*




Brian

Keith Thompson wrote:
> Mike <> writes:
>> i'm playing round with more child process code.
> [...]
>> can anyone explain? thanks.
>
> Why do you persist in posting to the wrong newsgroup?
>
Because we've been had old boy. Best of all, old Twinky boy's been had
good a proper!

--
Ian Collins

Mark McIntyre <> writes:

> Mike wrote:
>> Hi everybody
>>
>> i'm playing round with more child process code.
>>
>> this is a program straight from my textbook:
>>
>> void main(argv, argc)
>> int argc; char *argv[];
>
> You need to get a new text-book. This style of C is at least 30 years
> old and has been deprecated (ie obsolete) since the mid eighties.

I don't think it was deprecated then and it certainly was not
obsolete. Portable code had to use this style right up into the early
90s (and maybe even later). Your point is valid: it is an obsolete
style, but a 20-25 year old Unix book would have had to use it.

--
Ben.

Ben Pfaff wrote:
> Keith Thompson <kst-> writes:
>
>> Mike <> writes:
>>> void main(argv, argc)
>>> int argc; char *argv[];
>>> {
>> [...]
>>
>> What textbook are you using? The use of the old-style function
>> definition is excusable if it's a very old book; in that case, you
>> should get a newer one if at all possible. But the use of void as the
>> return type of main, though it's a common error, is harder to
>> understand. [...]
>
> Getting the return type of main wrong is only a nit, compared to
> getting its parameters in the wrong order!

Trolls just ain't what they used to be, are they?

--
Ian Collins

Keith Thompson <kst-> writes:

> Mike <> writes:
>> void main(argv, argc)
>> int argc; char *argv[];
>> {
> [...]
>
> What textbook are you using? The use of the old-style function
> definition is excusable if it's a very old book; in that case, you
> should get a newer one if at all possible. But the use of void as the
> return type of main, though it's a common error, is harder to
> understand. [...]

Getting the return type of main wrong is only a nit, compared to
getting its parameters in the wrong order!
--
"The way I see it, an intelligent person who disagrees with me is
probably the most important person I'll interact with on any given
day."
--Billy Chambless