sys/types.h文件

sys/types.h

       是Unix/Linux系统的基本系统数据类型的头文件，含有size_t，time_t，pid_t等类型。

      在应用程序源文件中包含 <sys/types.h> 以访问 _LP64 和 _ILP32 的定义。此头文件还包含适当时应使用的多个基本派生类型。尤其是以下类型更为重要：

　　clock_t 表示系统时间（以时钟周期为单位）。

　　dev_t 用于设备号。

　　off_t 用于文件大小和偏移量。

　　ptrdiff_t 是一种带符号整型，用于对两个指针执行减法运算后所得的结果。

　　size_t 反映内存中对象的大小（以字节为单位）。

　　ssize_t 供返回字节计数或错误提示的函数使用。

　　time_t 以秒为单位计时。

　　所有这些类型在 ILP32 编译环境中保持为 32 位值，并会在 LP64 编译环境中增长为 64 位值。

     blkcnt_t  Used for file block counts.

       blksize_t  Used for block sizes.

       clock_t  Used for system times in clock ticks or CLOCKS_PER_SEC; see <time.h> .

       clockid_t  Used for clock ID type in the clock and timer functions.

       dev_t  Used for device IDs.

       fsblkcnt_t
              Used for file system block counts.

       fsfilcnt_t
              Used for file system file counts.

       gid_t  Used for group IDs.

       id_t   Used as a general identifier; can be used to contain at least a pid_t, uid_t, or gid_t.

       ino_t  Used for file serial numbers.

       key_t  Used for XSI interprocess communication.

       mode_t Used for some file attributes.

       nlink_t  Used for link counts.

       off_t  Used for file sizes.

       pid_t  Used for process IDs and process group IDs.

       size_t Used for sizes of objects.

       ssize_t  Used for a count of bytes or an error indication.

       suseconds_t
              Used for time in microseconds.

       time_t Used for time in seconds.

       timer_t Used for timer ID returned by timer_create().

       trace_attr_t Used to identify a trace stream attributes object.

       trace_event_id_t  Used to identify a trace event type.

       trace_event_set_t  Used to identify a trace event type set.

       trace_id_t  Used to identify a trace stream.

       uid_t  Used for user IDs.

       useconds_t Used for time in microseconds.

       All of the types shall be defined as arithmetic types of an appropriate length, with the following exceptions:

       key_t
       Additionally:
* mode_t shall be an integer type.
* nlink_t, uid_t, gid_t, and id_t shall be integer types.
* blkcnt_t and off_t shall be signed integer types.
* fsblkcnt_t, fsfilcnt_t,   and ino_t shall be defined as unsigned integer types.
* size_t shall be an unsigned integer type.
* blksize_t, pid_t, and ssize_t shall be signed integer types.
* time_t and clock_t shall be integer or real-floating types.