Linux C 学习之 #include 的作用

#include <sys/types.h>

基本系统数据类型

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。linux编程中经常用到的头文件。

NAME
sys/types.h - data types

SYNOPSIS
#include <sys/types.h>

DESCRIPTION
The <sys/types.h> header shall include definitions for at least the following types:

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.