Declaring a Semaphore in Linux C

[rahul_shilps]

In Linux C Programming

I have a 'C' program of Producer-Consumer problem is solved through implementation of Semaphore.


PROGRAM::
------------------------------------------------------------------------------------------------------

#include<stdio.h>
#include<pthread.h>
#include<semaphore.h>
#include <sys/sem.h>


void cons();
void pro();

int buffer[5], rear=-1; front=0;

int main()
{
pthread_t t1, t2;

sem_init(&s, 0, 1);
sem_init(&n, 0, 0);
sem_init(&e, 0, 5);

pthread_create(&t1, NULL, (void *) cons, NULL);
pthread_create(&t2, NULL, (void *) pro, NULL);

pthread_join(t1, NULL);
pthread_join(t2, NULL);

sem_destroy(&s);
sem_destroy(&n);
sem_destroy(&e);

return(0);
}

void pro()
{
while (1)
{
int x;
sem_wait(&e);
sem_wait(&s);

x=random();
rear=(rear+1)%5);
buffer[rear]=x;
printf("Number produced at %d is %d", rear, buffer[rear]);

sem_post(&s);
sem_post(&n);

sleep(2);
}
}

void cons()
{
while(1)
{
sem_wait(&n);
sem-wait(&s);

printf ("Number consumed at %d is %d", front, buffer[front]);
front=((front+1)%5);

sem_post(&s);
sem_post(&e);

sleep(5);
}
}

------------------------------------------------------------------------------------------------------

In above program:
What is &s in the initialization of the semaphore?
What is 's'?

When I run my program it gives me error similar to:

****
error
****
5b.c: In function ‘main’:
5b.c:16: error: ‘s’ undeclared (first use in this function)
5b.c:16: error: (Each undeclared identifier is reported only once

****

How can I eliminate this error? I don't know much about semaphore.

Thank you.

[GNU-Fan]

This is not a problem with semaphores but a more fundamental error of not declaring/defining a variable you use.

[rahul_shilps]

how to declare that variable.

can u pleaze tell me

What will be the type of that variable 's'?

Thank you.

[aram535]

# man sem_init

will give you the decl and the type.