#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/sem.h>
int main( void )
{
union semun
{
int value; struct semid_ds *stat;
unsigned short int *array; struct seminfo *info;
 } control;
 key_t key;
 int flag,semid;
 struct sembuf sems;
 key = ftok( "/tmp",'k'+'m' ); flag = IPC_CREAT | S_IRUSR | S_IWUSR;
 semid = semget( key,1,flag);
 control.value =+1; semctl( semid,0x0,SETVAL,control );
sems.sem_num = 0; sems.sem_flg = 0x0;
switch( (int)fork() )
{
case -1: perror( "...fork()...\t" ); exit( 1 ); break;
case 0:
sems.sem_op =-1; semop( semid,&sems,1 );
printf( "...child...\t:%u\n",(unsigned)getpid() );
sems.sem_op =+2; semop( semid,&sems,1 );
break;
default:
sems.sem_op =-2; semop( semid,&sems,1 );
printf( "...master...\t:%u\n",(unsigned)getpid() );
sems.sem_op =+1; semop( semid,&sems,1 );
break;
}
semctl( semid,0x0,IPC_RMID );
return 0;
}