共享内存

共享内存头文件为shm.h

共享内存可以视为进程间通信速度最快的方式

共享内存实现函数非常简单，

shmctl shmget shmat shmdt 这四个函数是共享内存功能的核心函数

#  define __pid_t_defined
# endif
#endif	/* X/Open */


__BEGIN_DECLS

/* The following System V style IPC functions implement a shared memory
   facility.  The definition is found in XPG4.2.  */

/* Shared memory control operation.  */
extern int shmctl (int __shmid, int __cmd, struct shmid_ds *__buf) __THROW;

/* Get shared memory segment.  */
extern int shmget (key_t __key, size_t __size, int __shmflg) __THROW;

/* Attach shared memory segment.  */
extern void *shmat (int __shmid, const void *__shmaddr, int __shmflg)
     __THROW;

/* Detach shared memory segment.  */
extern int shmdt (const void *__shmaddr) __THROW;

__END_DECLS

#endif /* sys/shm.h */