would anyone help me this definition of func ptr?

[ooze]

In the unix like system, there is a func ptr signal defined as below
at the last line ,but I don't know
how to understand it. becoz the more general to define a func ptr is
the following
void (*signal)(int)
not
#include <signal.h>
void ( * signal(int SIG, void(*FUNC)(int )) )(int);

would anyone help me?
thanks much

[E. Robert Tisdale]

ooze wrote:

In the unix like system, there is a func ptr signal
defined as below at the last line but I don't know how to understand it.
becoz the more general to define a func ptr is the following:

void (*signal)(int); not #include <signal.h>
void ( * signal(int SIG, void(*FUNC)(int )) )(int); cat main.c #include <stdio.h>
#include <stdlib.h>
#include <signal.h>

void hello1(int signum) {
fprintf(stdout, "%d = signum\n", signum);
}

void hello2(int signum) {
fprintf(stdout, "%d = signum\n", signum);
}

int main(int argc, char* argv[]) {
typedef void (*sighandler_t) (int);
// install new signal handlers
sighandler_t oldUSR1sighandl er = signal(SIGUSR1, hello1);
sighandler_t oldUSR2sighandl er = signal(SIGUSR2, hello2);
while (EOF != getchar());
// restore old signal handlers
signal(SIGUSR2, oldUSR2sighandl er);
signal(SIGUSR1, oldUSR1sighandl er);
return EXIT_SUCCESS;
}
gcc -Wall -std=c99 -pedantic -o main main.c
./main
Then at a second terminal:
ps -a PID TTY TIME CMD
21080 pts/21 00:00:01 ssh
21217 pts/22 00:00:01 ssh
22016 pts/23 00:00:00 main
22018 pts/24 00:00:00 ps kill -s USR1 22016
and then, at the first terminal, I get:

10 = signum ./main
and back at the second terminal:
ps -a PID TTY TIME CMD
21080 pts/21 00:00:01 ssh
21217 pts/22 00:00:01 ssh
22027 pts/23 00:00:00 main
22028 pts/24 00:00:00 ps kill -s USR2 22027

and back, at the first terminal, I get:

12 = signum

[Barry Schwarz]

On 13 Jul 2004 18:21:58 -0700, fj***@163.net (ooze) wrote:

In the unix like system, there is a func ptr signal defined as below
at the last line ,but I don't know
how to understand it. becoz the more general to define a func ptr is
the following
void (*signal)(int)
not
#include <signal.h>
void ( * signal(int SIG, void(*FUNC)(int )) )(int);

would anyone help me?
thanks much

It helps to redistribute the white space

void(* signal(int SIG, void(*FUNC)(int )) )(int);

This is a function prototype and not the definition of a pointer.

signal is function (not a pointer) that

takes two parameters
an int (called SIG here but that is superfluous)
a pointer (called FUNC but also superfluous) to a function
that takes one parameter (int) and returns void

and returns a pointer to a function that takes an int and returns
void
<<Remove the del for email>>

[Emmanuel Delahaye]

In 'comp.lang.c', fj***@163.net (ooze) wrote:

In the unix like system, there is a func ptr signal defined as below
at the last line ,but I don't know
how to understand it. becoz the more general to define a func ptr is
the following
void (*signal)(int)
not
#include <signal.h>
void ( * signal(int SIG, void(*FUNC)(int )) )(int);

To make it simple, it's a function that returns a pointer to a function.
One of the parameter of the function is a pointer to a function. Probably the
most terrible syntax of the C language!

It is exactly the case where the use of a typedef is worthy.

typedef void F_TYPE (int);

F_TYPE *signal (int SIG, F_TYPE *FUNC);

--
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The C-language FAQ: http://www.eskimo.com/~scs/C-faq/top.html
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FAQ de f.c.l.c : http://www.isty-info.uvsq.fr/~rumeau/fclc/

[ooze]

Emmanuel Delahaye <em**********@n oos.fr> wrote in message news:<Xn******* *************** *****@212.27.42 .71>...

In 'comp.lang.c', fj***@163.net (ooze) wrote:

In the unix like system, there is a func ptr signal defined as below
at the last line ,but I don't know
how to understand it. becoz the more general to define a func ptr is
the following
void (*signal)(int)
not
#include <signal.h>
void ( * signal(int SIG, void(*FUNC)(int )) )(int);

To make it simple, it's a function that returns a pointer to a function.
One of the parameter of the function is a pointer to a function. Probably the
most terrible syntax of the C language!

It is exactly the case where the use of a typedef is worthy.

typedef void F_TYPE (int);

F_TYPE *signal (int SIG, F_TYPE *FUNC);

what's the differnce of the two declarations?

[ooze]

Emmanuel Delahaye <em**********@n oos.fr> wrote in message news:<Xn******* *************** *****@212.27.42 .71>...

In 'comp.lang.c', fj***@163.net (ooze) wrote:

In the unix like system, there is a func ptr signal defined as below
at the last line ,but I don't know
how to understand it. becoz the more general to define a func ptr is
the following
void (*signal)(int)
not
#include <signal.h>
void ( * signal(int SIG, void(*FUNC)(int )) )(int);

To make it simple, it's a function that returns a pointer to a function.
One of the parameter of the function is a pointer to a function. Probably the
most terrible syntax of the C language!

It is exactly the case where the use of a typedef is worthy.

typedef void F_TYPE (int);

F_TYPE *signal (int SIG, F_TYPE *FUNC);

what's the differnce of the two declarations?

[Emmanuel Delahaye]

In 'comp.lang.c', fj***@163.net (ooze) wrote:

OOH

> void ( * signal(int SIG, void(*FUNC)(int )) )(int);

OTOH
typedef void F_TYPE (int);

F_TYPE *signal (int SIG, F_TYPE *FUNC);

what's the differnce of the two declarations?

The point is that the semantic is the same, but the syntax is different. (It
tends to be clearer, well, I hope).

--
-ed- get my email here: http://marreduspam.com/ad672570
The C-language FAQ: http://www.eskimo.com/~scs/C-faq/top.html
C-reference: http://www.dinkumware.com/manuals/reader.aspx?lib=c99
FAQ de f.c.l.c : http://www.isty-info.uvsq.fr/~rumeau/fclc/