时间获取：
1. time
time_t time(time_t *tloc);功能：返回1970-01-01到现在的秒数（格林威治时间）
参数：
tloc:存放秒数空间首地址
返回值:
成功返回秒数
失败返回-1
2. localtime
struct tm *localtime(const time_t *timep);功能：讲秒数转换为本地时间
参数：
timep：存放秒数空间首地址
返回值：
成功返回结构体时间
失败返回NULL
struct tm {
int tm_sec; /* Seconds (0-60) */
int tm_min; /* Minutes (0-59) */
int tm_hour; /* Hours (0-23) */
int tm_mday; /* Day of the month (1-31) */
int tm_mon; /* Month (0-11) */
int tm_year; /* Year - 1900 */
int tm_wday; /* Day of the week (0-6, Sunday = 0) */
int tm_yday; /* Day in the year (0-365, 1 Jan = 0) */
int tm_isdst; /* Daylight saving time */
};3. mktime
time_t mktime(struct tm *tm);功能：将本地时间转换为秒数
举例应用：
获得本地当前的时间和秒数
#include <stdio.h>
#include <time.h>
int main(void)
{
time_t t;
struct tm *ptm = NULL;
struct tm pmk;
time(&t);
printf("%ld\n", t);
ptm = localtime(&t);
printf("%04d-%02d-%02d %02d:%02d:%02d\n", ptm->tm_year+1900, ptm->tm_mon+1,
ptm->tm_mday, ptm->tm_hour, ptm->tm_min, ptm->tm_sec);
pmk.tm_year = ptm->tm_year;
pmk.tm_mon = ptm->tm_mon;
pmk.tm_mday = ptm->tm_mday;
pmk.tm_hour = ptm->tm_hour;
pmk.tm_min = ptm->tm_min;
pmk.tm_sec = ptm->tm_sec;
t = mktime(&pmk);
printf("%ld\n", t);
return 0;
}
文件属性和权限的获取：
1.stat
int stat(const char *pathname, struct stat *statbuf);功能：将pathname对应的文件信息放入statbuf中
参数：
pathname:文件路径字符串的首地址
statbuf:存放文件信息空间的首地址
返回值：
成功返回0
失败返回-1
struct stat {
dev_t st_dev; /* ID of device containing file */
ino_t st_ino; /* Inode number */
mode_t st_mode; /* File type and mode */
nlink_t st_nlink; /* Number of hard links */
uid_t st_uid; /* User ID of owner */
gid_t st_gid; /* Group ID of owner */
dev_t st_rdev; /* Device ID (if special file) */
off_t st_size; /* Total size, in bytes */
blksize_t st_blksize; /* Block size for filesystem I/O */
blkcnt_t st_blocks; /* Number of 512B blocks allocated */
/* Since Linux 2.6, the kernel supports nanosecond
precision for the following timestamp fields.
For the details before Linux 2.6, see NOTES. */
struct timespec st_atim; /* Time of last access */
struct timespec st_mtim; /* Time of last modification */
struct timespec st_ctim; /* Time of last status change */
#define st_atime st_atim.tv_sec /* Backward compatibility */
#define st_mtime st_mtim.tv_sec
#define st_ctime st_ctim.tv_sec
};/etc/passwd 口令文件
/etc/group 组信息文件
2. getpwuid
struct passwd *getpwuid(uid_t uid);功能：通过UID获得对应的用户信息
参数：
uid:用户的ID号
返回值：
成功返回包含用户信息的结构体
失败返回NULL
struct passwd {
char *pw_name; /* username */
char *pw_passwd; /* user password */
uid_t pw_uid; /* user ID */
gid_t pw_gid; /* group ID */
char *pw_gecos; /* user information */
char *pw_dir; /* home directory */
char *pw_shell; /* shell program */
};3. getgrgid
struct group *getgrgid(gid_t gid);功能：通过组ID获得组信息
参数：
gid:组的ID号
返回值：
成功返回包含组信息的结构体
失败返回NULL
struct group {
char *gr_name; /* group name */
char *gr_passwd; /* group password */
gid_t gr_gid; /* group ID */
char **gr_mem; /* NULL-terminated array of pointers
to names of group members */
};4. readlink
ssize_t readlink(const char *pathname, char *buf, size_t bufsiz);功能：读取链接文件本身的内容
参数：
pathname:链接文件的路径
buf:存放数据空间首地址
bufsiz:最大存放数据字节数
返回值：
成功返回读到字节个数
失败返回-1
软链接和硬链接：
1. 软链接（符号链接）
通过文件名链接，所有能够看到的连接文件均为软连接文件
ln -s file.txt a.txt2. 硬链接：
通过文件对应的inode节点链接
ln file.txt b.txt
作业：
1. 编写程序实现ls -l的功能查看当前目录下所有文件的详细信息
#include "head.h"
int ListLstat(const char* pdirname);
int ListDir(void)
{
DIR *dp = NULL;
struct dirent *pp = NULL;
dp = opendir(".");
if(dp == NULL)
{
perror("fail to opendir");
return -1;
}
while(1)
{
pp = readdir(dp);
if(pp == NULL)
{
break;
}
if(*pp->d_name == '.')
{
continue;
}
ListLstat(pp->d_name);
}
closedir(dp);
return 0;
}
int ListLstat(const char *pdirname)
{
struct stat buf;
int ret = 0;
struct passwd *pwd = NULL;
struct group *gid = NULL;
struct tm *ptm = NULL;
char *mon[12] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
char linkbuff[1024] = {0};
ret = lstat(pdirname, &buf);
if(ret == -1)
{
perror("fail to lstat");
return -1;
}
switch(buf.st_mode & S_IFMT)
{
case S_IFBLK: putchar('b');break;
case S_IFCHR: putchar('c');break;
case S_IFDIR: putchar('d');break;
case S_IFREG: putchar('-');break;
case S_IFLNK: putchar('l');break;
case S_IFSOCK: putchar('s');break;
case S_IFIFO: putchar('p');break;
}
buf.st_mode & S_IRUSR ? putchar('r') : putchar('-');
buf.st_mode & S_IWUSR ? putchar('w') : putchar('-');
buf.st_mode & S_IXUSR ? putchar('x') : putchar('-');
buf.st_mode & S_IRGRP ? putchar('r') : putchar('-');
buf.st_mode & S_IWGRP ? putchar('w') : putchar('-');
buf.st_mode & S_IXGRP ? putchar('x') : putchar('-');
buf.st_mode & S_IROTH ? putchar('r') : putchar('-');
buf.st_mode & S_IWOTH ? putchar('w') : putchar('-');
buf.st_mode & S_IXOTH ? putchar('x') : putchar('-');
printf(" %ld", buf.st_nlink);
pwd = getpwuid(buf.st_uid);
if(pwd == NULL)
{
printf(" %d", buf.st_uid);
}
else
{
printf(" %s", pwd->pw_name);
}
gid = getgrgid(buf.st_gid);
if(gid == NULL)
{
printf(" %d", buf.st_gid);
}
else
{
printf(" %s", gid->gr_name);
}
printf(" %6ld", buf.st_size);
ptm = localtime(&buf.st_mtime);
printf(" %s %d %d:%d", mon[ptm->tm_mon], ptm->tm_mday, ptm->tm_hour, ptm->tm_min);
printf(" %s", pdirname);
if(S_ISLNK(buf.st_mode))
{
readlink(pdirname, linkbuff, sizeof(linkbuff));
printf(" -> %s", linkbuff);
}
printf("\n");
return 0;
}
int main(void)
{
ListDir();
return 0;
}
