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From: Vandana on 24 Feb 2010 17:27
Hello All,

When I compile the program below: I get the error,
main.c: In function ‘main’:
main.c:33: error: dereferencing pointer to incomplete type

Looks like the struct is not getting memory allocated. But I thought
this is happening throught the shmget/shmat calls. Am I wrong? I am
unable to understand this, could someone please explain this. Thank
you.

################
/*Sim.h*/
#ifndef SIM_H
#define SIM_H
#include <stdio.h>

struct sync_proc {
int parent_count;
int child_count;
int count;
int done;
};
extern struct sync_proc *sync_procs;
int sim_main(int core);
#endif
~
#########################

main.c
/* main.c */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/shm.h>
#include <sys/ipc.h>
#include <sys/wait.h>
#include <pthread.h>
#include "sim.h"


int main() {
struct sync_procs *sync_core;
pid_t pid;
int status;
key_t key;
key = 1045;
int shmidi;

if ((shmid = shmget(key, sizeof(struct sync_proc), IPC_CREAT |
0666)) < 0) {
perror("shmget");
exit(1);
}
printf("SHMID_opti::: %d\n", shmid);
sync_core = (struct sync_procs*) shmat(shmid, NULL, 0);

if (sync_core == (struct sync_procs*) -1) {
perror("shmat");
exit(1);
}

sync_core->count = 0; /* line producing the error */
pid = fork();
if (pid == 0 ) {
/* child process */
sim_main(0);
exit(0);
} else {
/* parent process */
sim_main(1);

wait(&status);
}
return 0;
}

##################
/* sim.c - does nothing for now */

#include <stdio.h>
int sim_main(int core) {

printf("From sim_main.c\n");
return 0;
}
~




From: Moi on 24 Feb 2010 17:39
On Wed, 24 Feb 2010 14:27:37 -0800, Vandana wrote:

> Hello All,
>
> When I compile the program below: I get the error, main.c: In
> function 'main':
> main.c:33: error: dereferencing pointer to incomplete type
>
> Looks like the struct is not getting memory allocated. But I thought
> this is happening throught the shmget/shmat calls. Am I wrong? I am
> unable to understand this, could someone please explain this. Thank you.
>
> ################
> /*Sim.h*/
> #ifndef SIM_H
> #define SIM_H
> #include <stdio.h>
>
> struct sync_proc {
> int parent_count;
> int child_count;
> int count;
> int done;
> };

[snip]

> printf("SHMID_opti::: %d\n", shmid);
> sync_core = (struct sync_procs*) shmat(shmid, NULL, 0);
>

sync_core = (struct sync_proc*) shmat(shmid, NULL, 0);

HTH,
AvK
From: Nicolas George on 24 Feb 2010 18:53
Vandana wrote in message
<60eea08c-0418-47d2-be51-76949a18bf88(a)s25g2000prd.googlegroups.com>:
> struct sync_proc {

> struct sync_procs *sync_core;

Trivial typo: sync_proc and sync_procs are not the same thing.
From: Nicolas George on 24 Feb 2010 18:57
Moi wrote in message
<7ffbd$4b85aa91$5350c024$29001(a)cache120.multikabel.net>:
> sync_core = (struct sync_proc*) shmat(shmid, NULL, 0);

sync_core = shmat(...);

Casting from void * is useless in C and may hide legitimate warnings, for
example if the header declaring shmat was forgotten and thus shmat got the
implicit int return type.
From: Vandana on 24 Feb 2010 19:14
Thanks a lot all, so stupid of me.
Sorry for wasting your time.


On Feb 24, 3:57 pm, Nicolas George <nicolas$geo...(a)salle-s.org> wrote:
> Moi  wrote in message
>
> <7ffbd$4b85aa91$5350c024$29...(a)cache120.multikabel.net>:
>
> > sync_core = (struct sync_proc*) shmat(shmid, NULL, 0);
>
> sync_core = shmat(...);
>
> Casting from void * is useless in C and may hide legitimate warnings, for
> example if the header declaring shmat was forgotten and thus shmat got the
> implicit int return type.

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