代码：

#include<stdio.h>
#include<sys/sem.h>
#include<sys/ipc.h>
#include<errno.h>
#include<string.h>
typedef int sem_t;
union semun{
int val;
struct semid_ds *buf;
unsigned short *array;
}arg;sem_t CreateSem(key_t key,int value)
{union semun sem;sem_t semid;sem.val=value;semid=semget(key,1,IPC_CREAT | 0777);
//	perror("error");if(-1==semid){
//	perror("error");printf("create semaphore error\n");return -1;}semctl(semid,0,SETVAL,sem);return	semid;
}
int Sem_P(sem_t semid)
{struct sembuf sops={0,+1,IPC_NOWAIT};return (semop(semid,&sops,1));
}
int Sem_V(sem_t semid)
{struct sembuf sops={0,-1,IPC_NOWAIT};return (semop(semid,&sops,1));
}
int GetvalueSem(sem_t semid)
{union semun sem;return semctl(semid,0,GETVAL,sem);
}
void DestroySem(sem_t semid)
{union semun sem;sem.val=0;semctl(semid,0,IPC_RMID,sem);
}
int main(void)
{key_t key;int semid;char i;struct semid_ds buf;int value =0;key=ftok("ipc/sem/",'a');printf("key = %d",key);semid=CreateSem(key,100);for(i=0;i<=3;i++){Sem_P(semid);Sem_V(semid);}value=GetvalueSem(semid);printf("sem value is:%d\n",value);DestroySem(semid);return 0;}

运行：