作用：
显示文件或文件系统的状态
头文件：
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
函数定义：
int stat(const char *path, struct stat *buf);
int fstat(int fd, struct stat *buf);
int lstat(const char *path, struct stat *buf);
stat() stats the file pointed to by path and fills in buf.
lstat() is identical to stat(), except that if path is a symbolic link,
then the link itself is stat-ed, not the file that it refers to.
fstat() is identical to stat(), except that the file to be stat-ed is
specified by the file descriptor fd.
stat结构体定义
struct stat {
dev_t st_dev; /* ID of device containing file */
ino_t st_ino; /* inode 号 */
mode_t st_mode; /* 保护位*/
nlink_t st_nlink; /* 硬链接号 */
uid_t st_uid; /* 用户ID uid */
gid_t st_gid; /* 组ID gid */
dev_t st_rdev; /* device ID (if special file) */
off_t st_size; /* total size, in bytes */
blksize_t st_blksize; /* blocksize for file system I/O */
blkcnt_t st_blocks; /* number of 512B blocks allocated */
(以下三个与时间相关)
time_t st_atime; /* time of last access */
time_t st_mtime; /* time of last modification */
time_t st_ctime; /* time of last status change */
};