Unix进程间通讯最常用的管道和信号量

无名管道
#include
#include
#include

#define INPUT 0
#define OUTPUT 1

int main()
{
        int file_pipe[2];
        pid_t pid;
        char buf[256];
        int count_pipe;
        pipe(file_pipe);  //无名管道
        if(!(pid = fork()))
        {
                printf("child output data!\n");
                close(file_pipe[INPUT]);
                write(file_pipe[OUTPUT], "aoyang", strlen("aoyang"));
          exit(0);
        }
        else if(pid > 0)
        {
                printf("father input data!\n");
                close(file_pipe[OUTPUT]);
                count_pipe = read(file_pipe[INPUT], buf, sizeof(buf));
                printf("%d bytes received from father: %s\n",count_pipe, buf);
        }
        return 0;
}
有名管道
mknod myfifo p

#include
void main()
{
        FILE * in_file;
        int count = 1;
        char buf[80];
        in_file = fopen("mypipe", "r");
        if (in_file == NULL)
        {
          printf("Error in fdopen.\n");
          exit(1);
        }
        while ((count = fread(buf, 1, 80, in_file)) > 0)
            printf("received from pipe: %s\n", buf);
        fclose(in_file);
}
#include
void main() {
        FILE * out_file;
        int count = 1;
        char buf[80];
        out_file = fopen("mypipe", "w");
        if (out_file == NULL)
        {
           printf("Error opening pipe.");
           exit(1);
        }
        sprintf(buf,"this is test data for the named pipe example\n");
        fwrite(buf, 1, 80, out_file);
        fclose(out_file);
}
信号量
#include
#include

 union semun{
  int   val;                                
  struct semid_ds *buf;          
  unsigned short *array;      
  struct   seminfo   *__buf;
 };
int main()
{
        key_t unique_key;
        int id;
        struct sembuf lock_it;
        union semun options;
        int i;
        unique_key = ftok(".", 'a'); //生成关键字
        id = semget(unique_key ,1, IPC_CREAT | IPC_EXCL | 0666);
        printf("semaphone id =%d\n", id);
        options.val = 1;
        semctl(id, 0, SETVAL, options);
       
        i = semctl(id, 0, GETVAL, 0);
  printf("value of semaphore at index 0 is %d\n", i);

  //
  lock_it.sem_num = 0; /*设置哪个信号量*/
  lock_it.sem_op = -1; /*定义操作*/
  lock_it.sem_flg = IPC_NOWAIT; /*操作方式*/
  if (semop(id, &lock_it, 1) == -1)
  {
          printf("can not lock semaphone.\n");
          exit(1);
  }
  i = semctl(id, 0, GETVAL, 0);
  printf("value of semaphore at index 0 is %d\n", i);
 
  semctl(id, 0, IPC_RMID, 0);
        return 0;
}