LinuxQuestions.org - errors when using semaphore

hi guys.

I don't get how to use semaphore in linux.

I am using ubuntu.

first of all, i have the following codes:

Code:

#include <semaphore.h>



sem_t sem;

int ret;

int count = 4;



/* to be shared among processes */

ret = sem_init(&sem, 1, count);

however when i complied the codes above, I got the following errors:

Code:

warning: data definition has no type or storage class

error: initializer element is not constant

what is wrong?

And another question, why can't I just use : semaphore mutex to declare?
like, semaphore mutex = 1;

thanks in advance.