文件相关命令

ps -aux|grep init?      //搜索包含init名称的进程
top                     //linux下的资源管理器（动态）//open 返回的int 是给后面的读/写/光标移动 用的fd，没有open就不能进行后面的操作；
int open(const char *pathname, int flags);
int open(const char *pathname, int flags, mode_t mode);
close(fd); //关闭文件// _t 都是返回的int数字；写write，读read，光标移动lseek
ssize_t write(int fd, const void *buf, size_t count);
ssize_t read(int fd, void *buf, size_t count);vimdiff demo1.c demo2.c //fopen注意mode就行，有:r r+ w w+ a ,返回的文件指针是给后面的读 写 偏移用
FILE *fopen(const char *pathname, const char *mode);
fclose(FILE *); //关闭文件//跟上面的差不多一样用
//fread/fwrite(读写的数组,读写的大小,  读写的最大次数?, 读写的文件指针)（读写返回次数的区别：读为有效次数，能一次读完就算你写10次，也返回只读1次）
size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream);
size_t fwrite(const void *ptr, size_t size, size_t nmemb,FILE *stream);
int fseek(FILE *stream, long offset, int whence);fputc();//写入一个字符；
fgetc();//读取一个字符
feof();/检测是否到达文件末尾，到了返回1；文件结束符为EOF=-1;//注意：读写操作都会使光标偏移，但也可以利用这点来遍历读写文件；
例：
while(!feof(FILE* fd)){printf("%c  ",fgetc(FILE* fd));

进程相关命令

getpid(); fork(); vfork();

//_t 一律返回的是int
//获取进程ID 就是pid
pid_t getpid(void);

//fork创建子进程
pid_t fork(void);
//这里返回的是的pid = 0 就是子进程，pid > 0 就是父进程；
//所以可以通过判断pid的值，来区别父子进程需要执行的代码；
//注意fork开辟的子进程，没有等待一说，父子进程谁抢到就先运行谁，
//【子进程为僵尸进程】；
//例：

    #include<stdio.h>#include <sys/types.h>#include <unistd.h>#include <stdlib.h>int main(){pid_t pid;int num = 0;pid = getpid();printf("this pid:%d\n",getpid());pid_t return_pid = fork();if(return_pid > 0){while(1){printf("this father pid:%d return_pid:%d \n",getpid(),return_pid);printf("father now num:%d\n",num);sleep(1);}}else if(return_pid == 0){printf("this son pid:%d return_pid:%d \n",getpid(),return_pid);num += 2;printf("child now num:%d\n",num);exit(6);}}

//vfork创建子进程
pid_t vfork(void);
//注意fork开辟的子进程，会等待子进程执行完并exit(num)后，父子进程才继续执行，
//【子进程不会成为僵尸进程】；
//例：

    #include<stdio.h>#include <sys/types.h>#include <unistd.h>#include <stdlib.h>int main(){pid_t pid;pid = getpid();printf("this pid:%d\n",getpid());int num = 0;printf("start_father_num:%d \n",num);pid_t return_pid = vfork();if(return_pid > 0){while(1){printf("this father pid:%d return_pid:%d \n",getpid(),return_pid);printf("num = %d\n",num);sleep(1);}}else if(return_pid == 0){int i;for(i=0;i<3;i++){printf("this son pid:%d return_pid:%d \n",getpid(),return_pid);num++;sleep(1);}exit(0);}return 0;}

exit(6);wait(status); WEXITSTATUS(status);

//wait() 返回的是子进程的ID 即pid；
//里面的 int *status 是子进程的exit(num)的num码；
//后续使用WEXITSTATUS(status),即可打印出来子进程退出时的状态码；
pid_t wait(int *status);
//例：

    #include <stdio.h>#include <sys/types.h>#include <unistd.h>#include <stdlib.h>int main(){pid_t pid;int status = 0;pid = getpid();printf("start father pid:%d\n",getpid());pid_t return_pid = fork();if(return_pid > 0 ){pid_t child_pid = wait(&status);printf("\n\nwait_return_childe_pid:%d\n",child_pid);printf("child exit code:%d \n",WEXITSTATUS(status));while(1){printf("this father pid:%d fork_return_pid:%d > 0  \n",getpid(),return_pid);sleep(1);}}else if(return_pid == 0){int i;for(i=0;i<3;i++){printf("this son pid:%d fork_return_pid:%d == 0 \n",getpid(),return_pid);}exit (6);}return 0;}

exec组函数 对比 system + popen ：

精彩博文跳转：

https://blog.csdn.net/u014530704/article/details/73848573

观后感：

跟着execl/execlp指定的程序跑了，不回来了！

//  date 获取时间的程序
execl("./PATH","date","NULL");
//  execl(程序所在路径,程序名,结尾必须为NULL)
//  就像这样用，在当前程序运行到这句代码时，
//  便将替换为后续执行execl所指的程序，不带回头的那种！execlp("date","date",NULL);
//  execlp(程序名,程序名,结尾必须为NULL)
//  就像这样用，它带p，能自己在环境变量下搜索对应的程序并替换后续执行；
//  也是不带回头的那种！

相比较之下 system 执行完指定程序后，还会回来，挺好！

system("cat demo1.c");
//执行完成后返回原程序，继续执行后续代码；

而对比popen 而言，popen除了将指定程序/代码执行完之后，继续执行后续代码外，还将读/写的内容放在管道内，并以文件指针的形式返回；

    #include <stdio.h>#include <unistd.h>int main(){printf("------------------------------------------------\nPS:\n");char* p = "ps";FILE *fd = popen(p,"r");char data[1024];fread(&data,1024,1,fd);printf("%s\n",data);perror("why");return 0;}

进程间通讯

精彩博文跳转

http://t.csdnimg.cn/xN2LT

观后感：

pipe 无名管道

int pipe(int pipefd[2]); (无名管道，在文件里看不到)

里面的fd[2]数组，其中 fd[0] : 读的fd， fd[1] : 写的fd；

//例：通过在父子进程中 close (fd[0]/fd[1]) 配合read(); write(); 实现进程间通讯；

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
int main()
{printf("------------------------------------------------:\n");int fd[2];int n_pipe = pipe(fd);char data1[128];if(n_pipe < 0){printf("error: can not creat pipe!\n");perror("why");}int pid = fork();if(pid < 0){printf("error: creat child failed!\n");perror("why");}if(pid > 0){// sleep(2);printf("this is father pc\n");close(fd[0]);write(fd[1],"hello pipe from father;",strlen("hello pipe from father;"));close(fd[1]);}if(pid == 0){printf("this is child pc\n");close(fd[1]);read(fd[0],data1,128);printf("data : %s\n",data1);exit(9);}return 0;
}

mkfifo 有名管道

//成功返回0；失败返回-1 设置erron = -1；
//返回值判断报错值：EEXIST，可以锁定报错为同名文件已存在目录中；
int mkfifo(const char *pathname, mode_t mode);
RETURN VALUE
On success mkfifo() and mkfifoat() return 0. In the case of
an error, -1 is returned (in which case, errno is set appro‐
priately).
EEXIST pathname already exists. This includes the case where
pathname is a symbolic link, dangling or not.

//例：

    #include<stdio.h>#include <errno.h>#include <sys/types.h>#include <sys/stat.h>int main(){if(mkfifo("./demo1.txt",0666) < 0 && errno == EEXIST ){printf("mkfifo error:\n");perror("why");}return 0;}

//mkfifo 配合 open read write 完成管道通讯；
//demo mkread：

    #include<stdio.h>#include <errno.h>#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include <string.h>#include <unistd.h>int main(){char buf[30]={0};int nff = mkfifo("./demo10.txt",0600);if(nff < 0 || errno == EEXIST ){printf("mkfifo error:\n");perror("why");}if(nff == 0){printf("mkfifo OK! \n");}int fd = open("./demo10.txt",O_RDONLY);printf("open success\n");int n_read = read(fd,buf,30);printf("read %d byte frome fifo context:\n%s\n",n_read,buf);int n_sys = system("rm ./demo10.txt");if(n_sys < 0 || n_sys ==127 ){printf("./demo10.txt delect error! \n");perror("why");}else{printf("\n--------------------------------------------");printf("\nsystem: ./demo10.txt delect success !\n");printf("--------------------------------------------\n");}close(fd);return 0;}

//demo mkwrite：

    #include<stdio.h>#include <errno.h>#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include <string.h>#include <unistd.h>int main(){char buf[30]={"hello mkfifo file_read/write"};int fd = open("./demo10.txt",O_WRONLY);printf("open success\n");int n_write = write(fd,buf,strlen(buf));printf("write %d byte frome fifo context:\n%s\n",n_write,buf);close(fd);return 0;}

消息队列

// 生成标准key 给后面msgget用；
// key_t ftok(const char *pathname, int proj_id);

// 获取msgid；
// int msgget(key_t key, int msgflg);

// 添加消息
// int msgsnd(int msqid, const void *msgp, size_t msgsz, int msgflg);

// 读取消息
// ssize_t msgrcv(int msqid, const void *msgp, size_t msgsz,long msgtyp, int msgflg);

// 控制消息队列 比如：杀掉消息队列
// int msgctl(int msqid, int cmd, struct msqid_ds *buf);

//杀掉消息队列 配合实现: msgctl(n_msgget,IPC_RMID,NULL);
// IPC_RMID

//例a：ftok_msgget_msgsnd_msgctl.c

    #include <stdio.h>#include <sys/types.h>#include <sys/ipc.h>#include <sys/msg.h>#include <string.h>struct NB {long msgtyp;char data[30];};int main(){struct NB ZDNB ={998,"Are you ok?"};printf("%ld\n",ZDNB.msgtyp);//key_t ftok(const char *pathname, int proj_id);        int key = ftok(".",6);printf("key = %x\n",key);//int msgget(key_t key, int msgflg);int n_get =  msgget(key, IPC_CREAT|0777);if(n_get >= 0){printf("msgget succes code:%d\n",n_get);perror("why");}else{printf("msgget error! code:%d\n",n_get);perror("why");}//int msgsnd(int msqid, const void *msgp, size_t msgsz, int msgflg);int snd = msgsnd(n_get,&ZDNB,sizeof(ZDNB.data),0);printf("msgsnd code:%d\n",snd);perror("why");struct NB ZDNB1;//ssize_t msgrcv(int msqid, const void *msgp, size_t msgsz,long msgtyp, int msgflg);int rcv = msgrcv(n_get,&ZDNB1,sizeof(ZDNB1.data),888,0);printf("msgrcv read code:%d\n",rcv);printf("--------------------------------------------\n");printf("read frome ./rcv_888 massege is:\n%s\n",ZDNB1.data);printf("--------------------------------------------\n");//int msgctl(int msqid, int cmd, struct msqid_ds *buf);int ctl = msgctl(n_get,IPC_RMID,NULL);printf("msgctl code:%d\n",ctl);perror("why");return 0;}

//例b：msgrcv.c

    #include<stdio.h>#include <sys/types.h>#include <sys/ipc.h>#include <sys/msg.h>#include <string.h>#include <unistd.h>struct NB {long msgtyp;char data[30];};int main(){struct NB ZNB1 ={888,"I am ok,Thank you!"};printf("%ld\n",ZNB1.msgtyp);struct NB ZNB;//key_t ftok(const char *pathname, int proj_id);        int key = ftok(".",6);printf("key = %x\n",key);//int msgget(key_t key, int msgflg);printf("key = %x\n",key);//int msgget(key_t key, int msgflg);int n_get =  msgget(key, IPC_CREAT|0777);if(n_get >= 0){printf("msgget succes code:%d\n",n_get);perror("why");}else{printf("msgget error! code:%d\n",n_get);perror("why");}//ssize_t msgrcv(int msqid, const void *msgp, size_t msgsz,long msgtyp, int msgflg);int rcv = msgrcv(n_get,&ZNB,sizeof(ZNB.data),998,0);printf("msgrcv read code:%d\n",rcv);printf("--------------------------------------------\n");printf("read frome ./snd_998 massege is:\n%s\n",ZNB.data);printf("--------------------------------------------\n");//int msgsnd(int msqid, const void *msgp, size_t msgsz, int msgflg);int snd = msgsnd(n_get,&ZNB1,sizeof(ZNB1.data),0);printf("msgsnd code:%d\n",snd);perror("why");sleep(1);//int msgctl(int msqid, int cmd, struct msqid_ds *buf);int ctl = msgctl(n_get,IPC_RMID,NULL);printf("msgctl code:%d\n",ctl);perror("why");return 0;}

共享内存_映射

// 生成标准key给shmget用；
// key_t ftok(const char *pathname, int proj_id);

// 生成共享内存ID；
// int shmget(key_t key, size_t size, int shmflg);

// 创建映射；通过共享内存ID; shmaddr 写 0；shmflg 写0；–均代表默认方式；
// void *shmat(int shmid, const void *shmaddr, int shmflg);
// int shmdt(const void *shmaddr); （不常用，因为没返回映射指针）

// 关闭映射；
// int shmdt(const void *shmaddr);

// 使用strcpy();写入映射；
// char *strcpy(char *dest, const char *src);
// char *strncpy(char *dest, const char *src, size_t n);

//printf(“”,);
// 查看当前共享内存映射
// ipcs -m;

// 杀掉共享内存映射ID；
// ipcrm -m shmID;

// 通过内存ID，删除共享文件的内存
// shmctl(shmid,IPC_RMID,0);

//例：shm_strcpy：

    #include <stdio.h>#include <sys/types.h>#include <sys/ipc.h>#include <sys/shm.h>#include <unistd.h>#include <string.h>int main(){int key = ftok(".",3);int shmid = shmget(key,1024*4,IPC_CREAT|0777);if(shmid < 0){printf("shmid error ! code:%d\n",shmid);perror("why");}char *shmaddr = shmat(shmid,0,0);char *cpy = strcpy(shmaddr,"hello shm friends!");printf("strcpy data to shm:\n%s\n",cpy);sleep(5);int dt = shmdt(shmaddr);if(dt >= 0){printf("shmdt code:%d\n",dt);perror("why");}shmctl(shmid,IPC_RMID,0);printf("quite\n");return 0;}

//例：shm_printf:

    #include <stdio.h>#include <sys/types.h>#include <sys/ipc.h>#include <sys/shm.h>#include <unistd.h>#include <string.h>int main(){int key = ftok(".",3);int shmid = shmget(key,1024*4,0);if(shmid < 0){printf("shmid error ! code:%d\n",shmid);perror("why");}char *shmaddr = shmat(shmid,0,0);printf("from shm data:\n%s\n",shmaddr);int dt = shmdt(shmaddr);if(dt > 0){printf("shmdt code:%d\n",dt);perror("why");}else{perror("why");}shmctl(shmid,IPC_RMID,0);printf("quite\n");return 0;}

信号编程

查看信号: kill -l

入门级 接收消息 signal signum

//sighandler_t signal(int signum, sighandler_t handler);
DESCRIPTION
signal() sets the disposition of the signal
signum to handler,
The signals SIGKILL and SIGSTOP cannot be caught
or ignored.

//例：

    #include <stdio.h>#include <signal.h>void handler(int signum){printf("signum:%d\n",signum);switch(signum){case 2:printf("SIGINT\n");break;case 9:printf("SIGKILL\n");break;}}int main(){signal(SIGINT,handler);signal(SIGKILL,handler);while(1);return 0;}

入门级 发送信号 实现杀进程 kill -9 pid

//例：

    #include <stdio.h>#include <signal.h>#include <stdlib.h>int main(int argc,char **argv){int num = atoi(argv[1]);int pid = atoi(argv[2]);char buf[30] = {0};sprintf(buf,"kill %d %d",num,pid);system(buf);return 0;}

高级 sigaction 接受信号_携带消息

    #include <stdio.h>#include <signal.h>#include <sys/types.h>#include <unistd.h>//void handler(int sig, siginfo_t *info, void *ucontext)void handler(int signum, siginfo_t *info, void *ucontext){printf("get signum:%d\n",signum);if(ucontext != NULL){printf("get data:%d\n",info->si_int);printf("get data:%d\n",info->si_value.sival_int);printf("frome pid:%d\n",info->si_pid);}}int main(){/*struct sigaction {void     (*sa_handler)(int);void     (*sa_sigaction)(int, siginfo_t *, void *); //if sa_flags = SA_SIGINFO, setthere it is handler;sigset_t   sa_mask;int        sa_flags; //SA_SIGINFO able get sig;void     (*sa_restorer)(void);};*/struct sigaction act;act.sa_flags = SA_SIGINFO;act.sa_sigaction = handler;printf("getpid:%d\n",getpid());//int sigaction(int signum, const struct sigaction *act, struct sigaction *oldact);sigaction(SIGUSR1,&act,NULL);while(1);return 0;}

高级 sigqueue 发送信号_携带消息

    #include <stdio.h>#include <signal.h>#include <stdlib.h>#include <sys/types.h>#include <unistd.h>int main(int argc,char** argv){//moren have /*union sigval {int   sival_int;void *sival_ptr;};*/int pid = atoi(argv[2]);int signum = atoi(argv[1]);union sigval value;value.sival_int = 666;printf("getpid:%d\n",getpid());//int  sigqueue(pid_t  pid, int signum, const union sigval value);int que = sigqueue(pid,signum,value);if(que >= 0){printf("send int data success!\n");}else{perror("why");}return 0;}

信号量编程

信号量（semaphore）与IPC 结构不同，它是一个计数器。信号量用于实现进程间的互斥与同步，而不是用于存储进程间通信数据。

信号量用于进程间同步，若要在进程间传递数据需要结合共享内存。
信号量基于操作系统的 PV 操作，程序对信号量的操作都是原子操作。
每次对信号量的 PV 操作不仅限于对信号量值加 1 或减 1，而且可以加减任意正整数。
支持信号量组。

//例：通过信号量+/-1，实现父子进程，执行顺序控制；

#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <unistd.h>union semun {int              val;    /* Value for SETVAL */struct semid_ds *buf;    /* Buffer for IPC_STAT, IPC_SET */unsigned short  *array;  /* Array for GETALL, SETALL */struct seminfo  *__buf;  /* Buffer for IPC_INFO(Linux-specific) */
};// EXAMPLE
// The following code segment uses semop() to atomically wait  for  the
// value  of  semaphore  0 to become zero, and then increment the sema‐
// phore value by one.//     struct sembuf sops[2];
//     int semid;//     /* Code to set semid omitted *///     sops[0].sem_num = 0;        /* Operate on semaphore 0 */
//     sops[0].sem_op = 0;         /* Wait for value to equal 0 */
//     sops[0].sem_flg = 0;//     sops[1].sem_num = 0;        /* Operate on semaphore 0 */
//     sops[1].sem_op = 1;         /* Increment value by one */
//     sops[1].sem_flg = 0;//     if (semop(semid, sops, 2) == -1) {
//         perror("semop");
//         exit(EXIT_FAILURE);
//     }void pGetKey( int semid) //拿锁/信号量
{struct sembuf set;//int semop(int semid, struct sembuf *sops, size_t nsops);set.sem_num = 0;        /* Operate on semaphore 0 */set.sem_op = -1;         //对信号量的值-1，拿掉一个锁；set.sem_flg = SEM_UNDO;  //在进程终止时自动释放所持有的信号量资源//释放/公布盒子位置；semop(semid, &set, 1);printf("get_key sem success!\n");
}void vPutBackKey( int semid) //还锁/信号量
{struct sembuf set;//int semop(int semid, struct sembuf *sops, size_t nsops);set.sem_num = 0;        /* Operate on semaphore 0 */set.sem_op = 1;         //对信号量的值+1，还一个锁；set.sem_flg = SEM_UNDO;  //在进程终止时自动释放所持有的信号量资源//释放/公布盒子位置；semop(semid, &set, 1);printf("back_key sem success!\n\n");
}int main()
{int key = ftok(".",2);//int semget(key_t  key,nsems, int semflg);//获取/创建 1个信号量/1个盒子；int semid = semget (key,1,IPC_CREAT|0666);union semun initsem;initsem.val = 0; //起始信号量的值位0；盒子0个锁；//int semctl(int semid, int semnum, int cmd, ...);//如果要SETVAL设置信号量的值，需要多加个联合体变量initsem；semctl(semid,0,SETVAL,initsem);int pid = fork();if(pid > 0){//去拿锁，但一开始盒子里没有锁，所以就先执行子进程放锁；pGetKey(semid); printf("is father pid:%d\n",pid);//用完了，再把锁放回盒子；vPutBackKey(semid);//不需要设值，则3个变量即可，关掉信号量；semctl(semid,0,IPC_RMID);}else if(pid == 0){printf("is child pid:%d\n",pid);//子进程放锁进去；vPutBackKey(semid);        }else{printf("fork error! code:%d\n",pid);perror("why");}return 0;
}

信号量+共享内存 实现进程通讯

//例：（双信号量实现）

//双信号量发送端：

#include <sys/sem.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <unistd.h>
#include <string.h>union semun {int              val;    /* Value for SETVAL */struct semid_ds *buf;    /* Buffer for IPC_STAT, IPC_SET */unsigned short  *array;  /* Array for GETALL, SETALL */struct seminfo  *__buf;  /* Buffer for IPC_INFO(Linux-specific) */
};void pGetKey( int semid,int num) //拿锁/信号量
{struct sembuf set;//int semop(int semid, struct sembuf *sops, size_t nsops);set.sem_num = num;        /* Operate on semaphore 0 */set.sem_op = -1;         //对信号量的值-1，拿掉一个锁；set.sem_flg = SEM_UNDO;  //在进程终止时自动释放所持有的信号量
资源//释放/公布盒子位置；semop(semid, &set, 1);printf("get_key sem success!\n");
}void vPutBackKey( int semid,int num) //还锁/信号量
{struct sembuf set;//int semop(int semid, struct sembuf *sops, size_t nsops);set.sem_num = num;        /* Operate on semaphore 0 */set.sem_op = 1;         //对信号量的值+1，还一个锁；set.sem_flg = SEM_UNDO;  //在进程终止时自动释放所持有的信号量
资源//释放/公布盒子位置；semop(semid, &set, 1);printf("back_key sem success!\n\n");
}
int main()
{//shmget use keyint key = ftok(".",3);int shmid = shmget(key,1024*4,IPC_CREAT|0777);//semget use key2int key2 = ftok(".",2);//int semget(key_t  key,nsems, int semflg);//获取/创建 2个信号量；//control控制 rd_wrint semid = semget (key2,2,IPC_CREAT|0666);//semid是信号集id；union semun initsem;union semun initsem2;initsem.val = 1; //信号量1的值1；1个锁；initsem2.val = 0;//信号量2的值0；0个锁；//int semctl(int semid, int semnum, int cmd, ...);//如果要SETVAL设置信号量的值，需要多加个联合体变量initsem；//initsem no.0 semctl(semid,0,SETVAL,initsem);semctl(semid,1,SETVAL,initsem2);pGetKey(semid,0);if(shmid < 0){printf("shmid error ! code:%d\n",shmid);perror("why");}char *shmaddr = shmat(shmid,0,0);char *cpy = strcpy(shmaddr,"hello _sem_shm friends!");printf("snd data:\n%s\n",cpy);int dt = shmdt(shmaddr);if(dt >= 0){printf("shmdt code:%d\n",dt);perror("why");}vPutBackKey(semid,1);shmctl(shmid,IPC_RMID,0);semctl(semid,0,IPC_RMID);semctl(semid,1,IPC_RMID);printf("quite\n");return 0;
}        

//双信号量接收端：

#include <sys/sem.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <unistd.h>
#include <string.h>union semun {int              val;    /* Value for SETVAL */struct semid_ds *buf;    /* Buffer for IPC_STAT, IPC_SET */unsigned short  *array;  /* Array for GETALL, SETALL */struct seminfo  *__buf;  /* Buffer for IPC_INFO(Linux-specific) */
};void pGetKey( int semid,int num) //拿锁/信号量
{struct sembuf set;//int semop(int semid, struct sembuf *sops, size_t nsops);set.sem_num = num;        /* Operate on semaphore 0 */set.sem_op = -1;         //对信号量的值-1，拿掉一个锁；set.sem_flg = SEM_UNDO;  //在进程终止时自动释放所持有的信号量
资源//释放/公布盒子位置；semop(semid, &set, 1);printf("get_key sem success!\n");
}void vPutBackKey( int semid,int num) //还锁/信号量
{struct sembuf set;//int semop(int semid, struct sembuf *sops, size_t nsops);set.sem_num = num;        /* Operate on semaphore 0 */set.sem_op = 1;         //对信号量的值+1，还一个锁；set.sem_flg = SEM_UNDO;  //在进程终止时自动释放所持有的信号量
资源//释放/公布盒子位置；semop(semid, &set, 1);printf("back_key sem success!\n\n");
}
int main()
{//shmget use keyint key = ftok(".",3);int shmid = shmget(key,1024*4,IPC_CREAT|0777);//semget use key2int key2 = ftok(".",2);//int semget(key_t  key,nsems, int semflg);//获取/创建 2个信号量；//control控制 rd_wrint semid = semget (key2,2,IPC_CREAT|0666);//semid是信号集id；union semun initsem;union semun initsem2;initsem.val = 1; //信号量1的值1；1个锁；initsem2.val = 0;//信号量2的值0；0个锁；//int semctl(int semid, int semnum, int cmd, ...);//如果要SETVAL设置信号量的值，需要多加个联合体变量initsem；//initsem no.0 semctl(semid,0,SETVAL,initsem);semctl(semid,1,SETVAL,initsem2);pGetKey(semid,1);char *shmaddr = shmat(shmid,0,0);printf("from shm data:\n%s\n",shmaddr);int dt = shmdt(shmaddr);if(dt > 0){printf("shmdt code:%d\n",dt);perror("why");}else{perror("why");}vPutBackKey(semid,0);printf("quite\n");return 0;
}

//例：（单信号量实现）

//单信号量发送端：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/shm.h>#define KEY 1234// 定义共享内存结构
struct shared_memory {int data;
};// 定义信号量操作结构
struct sembuf sem_op;int main() {int shm_id, sem_id;struct shared_memory *shm_ptr;// 创建共享内存shm_id = shmget(KEY, sizeof(struct shared_memory), IPC_CREAT | 0666);if (shm_id == -1) {perror("shmget");exit(1);}// 连接共享内存shm_ptr = (struct shared_memory *)shmat(shm_id, NULL, 0);if (shm_ptr == (struct shared_memory *)(-1)) {perror("shmat");exit(1);}// 创建信号量sem_id = semget(KEY, 1, IPC_CREAT | 0666);if (sem_id == -1) {perror("semget");exit(1);}// 初始化信号量semctl(sem_id, 0, SETVAL, 1);// 写入数据到共享内存shm_ptr->data = 42;// 通过信号量控制读进程的访问sem_op.sem_num = 0;sem_op.sem_op = 1;  // 增加信号量值sem_op.sem_flg = 0;semop(sem_id, &sem_op, 1);// 分离共享内存shmdt(shm_ptr);return 0;
}

//单信号量发送端：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/shm.h>#define KEY 1234// 定义共享内存结构
struct shared_memory {int data;
};// 定义信号量操作结构
struct sembuf sem_op;int main() {int shm_id, sem_id;struct shared_memory *shm_ptr;// 创建共享内存shm_id = shmget(KEY, sizeof(struct shared_memory), IPC_CREAT | 0666);if (shm_id == -1) {perror("shmget");exit(1);}// 连接共享内存shm_ptr = (struct shared_memory *)shmat(shm_id, NULL, 0);if (shm_ptr == (struct shared_memory *)(-1)) {perror("shmat");exit(1);}// 创建信号量sem_id = semget(KEY, 1, IPC_CREAT | 0666);if (sem_id == -1) {perror("semget");exit(1);}// 通过信号量等待写进程完成写入sem_op.sem_num = 0;sem_op.sem_op = -1;  // 减少信号量值sem_op.sem_flg = 0;semop(sem_id, &sem_op, 1);// 读取共享内存中的数据printf("Data read from shared memory: %d\n", shm_ptr->data);// 分离共享内存shmdt(shm_ptr);// 删除共享内存和信号量shmctl(shm_id, IPC_RMID, NULL);semctl(sem_id, 0, IPC_RMID);return 0;
}

更新日志

23/10/27：使用markdown编写.md格式，增加目录，更新内容：a.信号量；b.信号量+共享内存实现进程通讯；