shmget problem

Good evening,

I'm trying to allocated share memory and i get the error

sh.c: In function `main':
sh.c:14: error: parse error before ';' token

My program is like that :

Code:

#define SHMSZ 40;

int main() {

key_t key;
int shmid;

if((key = ftok("path of user", 0)) < 0){
printf("\n%d Error in key\n",key);
return 0;
}

printf("%d\n",key);


shmid = shmget(key,SHMSZ,(IPC_CREAT | 0666));

/* the error appears here inside shmget*/

}

What do i do wrong?
Thanks, in advance!

Where is shmget() declared?

Well, i have included the libraries :

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdio.h>
#include<time.h>
#include <unistd.h>

Well putting a ; on the end of your #define is usually the wrong thing to do.

Your use expands to
shmid = shmget(key,40;,(IPC_CREAT | 0666));

Unbelievable!
This was the error and I have spent 1 and a half hour to see what was going wrong and it was only a ';'!
Thanks very much!

Goodd evening,

I would like to ask you sthg as far as dividing a shared memory segment into
8 buffers is concerned.

e.g. in the following code , we have allocated the shared memory segment and we want now to divide it into 8 stacks which every stack is going to consist of 4 integers.(4 * 8 =32 integers)
How do we do that?

Code:

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdio.h>
#include<time.h>
#include <unistd.h>

#define SHMSZ 8

int main() {

key_t key;
int shmid;
int *buf;

if((key = ftok("path of user", 0)) < 0){
printf("\n%d Error in key\n",key);
return 0;
}

printf("%d\n",key);


shmid = shmget(key,SHMSZ * sizeof(int),(IPC_CREAT | 0666));


buf = shmat(shmid,NULL,0);


}

Thanks, in advance!

Isn't that just taking a 32*sizeof(int) block of memory and dividing it into 8 ? Aka having one pointer point to the beginning of the block, another 4 integers further, and then another 4 integers further, and so on ?

Originally Posted by Happy_Reaper

Isn't that just taking a 32*sizeof(int) block of memory and dividing it into 8 ? Aka having one pointer point to the beginning of the block, another 4 integers further, and then another 4 integers further, and so on ?

Well,i need to have for every buffer 3 semaphores which are going to check if the buffer is full,empty or no other process tries to have access to this buffer,this means that i must have 8 * 3 = 24 semaphores.

Do you have any idea how i can utilise that?

Thanks, in advance!

Right, you can do that in similar fashion, either in a seperate block or by making your original block bigger by 24 * sizeof(semaphore).