//管道的性质就是，一个进程的输出作为另一个进程的输入
//那么我们可以关闭一个进程读端使之作为输入端，
//另一个进程关闭写端，读取数据，接收数据作为管道输出端//FIFO命名管道
//文件系统中，命名管道是特殊文件的方式存在的
//不同进程可以通过命名管道共享数据//命名管道一直是阻塞方式的，且必须是显示的通过open建立连接到管道的通道
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<unistd.h>#include<sys/types.h>int main()
{int result = 1;int fd[2];pid_t pid;int *write_fd = &fd[1];        //写文件描述int *read_fd = &fd[0];        //读文件描述int nbytes;char str[] = "管道，你好\n";    char readBuffer[80];memset(readBuffer,0,sizeof(readBuffer));result = pipe(fd);        //创建管道if(-1==result){printf("管道创建失败！\n");return -1;}pid = fork();            //进程创建分叉程序if(-1 == pid){printf("fork失败");return -1;}if(0==pid)            //子进程关闭读端，写入字符
    {close(*read_fd);result = write(*write_fd,str,strlen(str));printf("写入%d个数据\n",result);}else                //父进程关闭写端，读取数据
    {close(*write_fd);nbytes = read(*read_fd,readBuffer,sizeof(readBuffer));printf("接收到%d个数据，内容为%s",nbytes,readBuffer);}return 0;
}

//file： msg.h/* message buffer for msgsnd and msgrcv calls */
struct msgbuf {__kernel_long_t mtype;          /* type of message */char mtext[1];                  /* message text */
};/* Obsolete, used only for backwards compatibility and libc5 compiles */
struct msqid_ds {struct ipc_perm msg_perm;struct msg *msg_first;        /* first message on queue,unused  */struct msg *msg_last;        /* last message in queue,unused */__kernel_time_t msg_stime;    /* last msgsnd time */__kernel_time_t msg_rtime;    /* last msgrcv time */__kernel_time_t msg_ctime;    /* last change time */unsigned long  msg_lcbytes;    /* Reuse junk fields for 32 bit */unsigned long  msg_lqbytes;    /* ditto */unsigned short msg_cbytes;    /* current number of bytes on queue */unsigned short msg_qnum;    /* number of messages in queue */unsigned short msg_qbytes;    /* max number of bytes on queue */__kernel_ipc_pid_t msg_lspid;    /* pid of last msgsnd */__kernel_ipc_pid_t msg_lrpid;    /* last receive pid */
};

//filename/* Obsolete, used only for backwards compatibility and libc5 compiles */
struct ipc_perm
{__kernel_key_t    key;　　//函数msgget()使用的键值　　__kernel_uid_t    uid;　　//用户UID__kernel_gid_t    gid;　　//用户GID__kernel_uid_t    cuid;　　//创建者UID__kernel_gid_t    cgid;　　//创建者GID__kernel_mode_t    mode; 　　//权限unsigned short    seq;　　//序列号
};

//filename sys/sem.h/* arg for semctl system calls. */
union semun {int val;            /* value for SETVAL */struct semid_ds *buf;    /* buffer for IPC_STAT & IPC_SET */unsigned short *array;    /* 数组结构 */struct seminfo *__buf;    /* 信号量内部结构 */void *__pad;
};

#include<stdio.h>
#include<unistd.h>
#include<sys/ipc.h>
#include<sys/sem.h>
#include<sys/types.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,0,IPC_CREAT);if(-1 == semid){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));
}void SetvalueSem(sem_t semid , int value)
{union semun sem;sem.val = value;semctl(semid,0,SETVAL,sem);
}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()
{key_t key;int semid;char i;int value = 0;key = ftok("/ipc/sem",'a');semid = CreateSem(key,100);for( i = 0;i <= 3;++i){Sem_P(semid);Sem_V(semid);    }value = GetvalueSem(semid);    DestroySem(semid);    return 0;
}