Linux下编程-----文件与IO（二）stat函数

功能:获取文件元数据

 #include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>
 int stat(const char *path, struct stat *buf);
 int fstat(int fd, struct stat *buf);
 int lstat(const char *path, struct stat *buf);

stat结构体

 struct stat
 {
     dev_t     st_dev;     /* ID of device containing file */
     ino_t     st_ino;     /* inode number */
     mode_t    st_mode;    /* protection */
     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; /* blocksize for filesystem I/O */
     blkcnt_t  st_blocks;  /* number of 512B blocks allocated */
     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 */
 };

 //示例   - err_exit函数如前
 // 其实可以通过Linux 系统调用major, minor来替换(如下)
 #define MAJOR(a) (int)((unsigned short)a >> 8)  //主设备号: 获取高8位
 #define MINOR(a) (int)((unsigned short)a & 0xFF)//次设备号: 获取低8位
 bool fileType(const struct stat &fileStat);
 void filePerm(const struct stat &fileStat, char *perm);

 int main(int argc, char *argv[])
 {
     if (argc != 2)
     {
         cerr << "Usage: " << argv[0] << " <file-name>" << endl;
         exit(EXIT_FAILURE);
     }

     struct stat fileStat;
     if (lstat(argv[1], &fileStat) == -1)
         err_exit("stat error");

     cout << "file-name: " << argv[1] << endl;
     cout << "st_ino = " << fileStat.st_ino << endl;
     cout << "device major: " << major(fileStat.st_dev)
          << ", minor: " << minor(fileStat.st_dev) << endl;
     if (fileType(fileStat))
     {
         cout << "----------------------------" << endl;
         cout << "major: " << MAJOR(fileStat.st_dev)
              << ", minor: " << MINOR(fileStat.st_rdev) << endl;
 //        cout << "major: " << major(fileStat.st_dev)
 //             << ", minor: " << minor(fileStat.st_rdev) << endl;
     }
     //获取文件的权限: 但要注意需要&上07777
     fprintf(stdout, "file permission: %o", fileStat.st_mode&07777);
     char perm[11];
     filePerm(fileStat, perm);
     cout << ", msg: " << perm << endl;

     cout << "st_nlink = " << fileStat.st_nlink << endl;
     cout << "st_uid = " << fileStat.st_uid << endl;
     cout << "st_gid = " << fileStat.st_gid << endl;
     cout << "st_size = " << fileStat.st_size << endl;
     cout << "st_blksize = " << fileStat.st_blksize << endl;
     cout << "st_blocks = " << fileStat.st_blocks << endl;
     cout << "st_atime = " << fileStat.st_atime << endl;
     cout << "st_ctime = " << fileStat.st_ctime << endl;
     cout << "st_mtime = " << fileStat.st_mtime << endl;
 }

 bool fileType(const struct stat &fileStat)
 {
     cout << "file-type: ";
     switch(fileStat.st_mode & S_IFMT)
     {
     case S_IFSOCK:
         cout << "socket";
         break;
     case S_IFLNK:
         cout << "symbolic link";
         break;
     case S_IFREG:
         cout << "regular file";
         break;
     case S_IFBLK:
         cout << "block device" << endl;
         return true;
         break;
     case S_IFDIR:
         cout << "directory";
         break;
     case S_IFCHR:
         cout << "character device" << endl;
         return true;
         break;
     case S_IFIFO:
         cout << "FIFO" << endl;
         break;
     default:
         cout << "unknown?";
         break;
     }
     cout << endl;
     return false;
 }

 void filePerm(const struct stat &fileStat, char *perm)
 {
     strcpy(perm, "----------");
     switch(fileStat.st_mode & S_IFMT)
     {
     case S_IFSOCK:
         perm[0] = 's';
         break;
     case S_IFLNK:
         perm[0] = 'l';
         break;
     case S_IFREG:
         perm[0] = '-';
         break;
     case S_IFBLK:
         perm[0] = 'b';
         break;
     case S_IFDIR:
         perm[0] = 'd';
         break;
     case S_IFCHR:
         perm[0] = 'c';
         break;
     case S_IFIFO:
         perm[0] = 'p';
         break;
     default:
         perm[0] = '?';
         break;
     }

     if (fileStat.st_mode & S_IRUSR)
         perm[1] = 'r';
     if (fileStat.st_mode & S_IWUSR)
         perm[2] = 'w';
     if (fileStat.st_mode & S_IXUSR)
         perm[3] = 'x';
     if (fileStat.st_mode & S_IRGRP)
         perm[4] = 'r';
     if (fileStat.st_mode & S_IWGRP)
         perm[5] = 'w';
     if (fileStat.st_mode & S_IXGRP)
         perm[6] = 'x';
     if (fileStat.st_mode & S_IROTH)
         perm[7] = 'r';
     if (fileStat.st_mode & S_IWOTH)
         perm[8] = 'w';
     if (fileStat.st_mode & S_IXOTH)
         perm[9] = 'x';
 }

实现ls -l的功能：

【拓展函数】

1.getpwuid 

 struct passwd *getpwuid(uid_t uid);

 //passwd结构体
 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 */
 };

2.getgrgid

 struct group *getgrgid(gid_t gid);

 //group结构体
 struct group
 {
     char   *gr_name;       /* group name */
     char   *gr_passwd;     /* group password */
     gid_t   gr_gid;        /* group ID */
     char  **gr_mem;        /* group members */
 };

3. readlink

 ssize_t readlink(const char *path, char *buf, size_t bufsiz);

4. localtime

 struct tm *localtime(const time_t *timep);

 //tm结构体
 struct tm
 {
     int tm_sec;         /* seconds */
     int tm_min;         /* minutes */
     int tm_hour;        /* hours */
     int tm_mday;        /* day of the month */
     int tm_mon;         /* month */
     int tm_year;        /* year */
     int tm_wday;        /* day of the week */
     int tm_yday;        /* day in the year */
     int tm_isdst;       /* daylight saving time */
 };

 //示例: 实现简单的ls -l功能
 #include <iostream>

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <string.h>

 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <unistd.h>
 #include <grp.h>
 #include <pwd.h>
 #include <time.h>

 using namespace std;

 inline void err_exit(std::string message);
 bool isDevice(const struct stat &fileStat);
 bool isLink(const struct stat &fileStat);
 void filePerm(const struct stat &fileStat, char *perm);

 int main(int argc, char *argv[])
 {
     if (argc != 2)
     {
         cerr << "Usage: " << argv[0] << " <file-name>" << endl;
         exit(EXIT_FAILURE);
     }

     struct stat fileStat;
     if (lstat(argv[1], &fileStat) == -1)
         err_exit("lstat error");

     //获取权限
     char perm[11];
     filePerm(fileStat, perm);
     cout << perm << ' ';

     //获取文件链接数
     cout << fileStat.st_nlink << ' ';

     //获取文件所有者
     struct passwd *ps = getpwuid(fileStat.st_uid);
     cout << ps->pw_name << ' ';

     //获取文件所属组
     struct group *gp = getgrgid(fileStat.st_gid);
     cout << gp->gr_name << ' ';

     if (isDevice(fileStat))
         cout << major(fileStat.st_dev) << ", "
              << minor(fileStat.st_rdev) << ' ';
     else
         cout << fileStat.st_size << ' ';

     // 打印最后一次修改时间
     time_t mtime = fileStat.st_mtime;
     struct tm *pTime = localtime(&mtime);
     cout << pTime->tm_mon+1 << "月 " << pTime->tm_mday << ' '
          << pTime->tm_hour << ':' << pTime->tm_min << ' ';

     // 打印文件名
     cout << argv[1];
     if (isLink(fileStat))
     {
         cout << " -> ";
         char name[1024] = {0};
         if (readlink(argv[1], name, sizeof(name)) == -1)
             err_exit("readlink error");
         cout << name;
     }
     cout << endl;

 }

 inline void err_exit(std::string message)
 {
     perror(message.c_str());
     exit(EXIT_FAILURE);
 }

 bool isDevice(const struct stat &fileStat)
 {
     switch(fileStat.st_mode & S_IFMT)
     {
     case S_IFBLK:
     case S_IFCHR:
         return true;
         break;
     default:
         return false;
         break;
     }
     return false;
 }

 bool isLink(const struct stat &fileStat)
 {
     if ((fileStat.st_mode & S_IFMT) == S_IFLNK)
         return true;
     return false;
 }

 void filePerm(const struct stat &fileStat, char *perm)
 {
     strcpy(perm, "----------");
     switch(fileStat.st_mode & S_IFMT)
     {
     case S_IFSOCK:
         perm[0] = 's';
         break;
     case S_IFLNK:
         perm[0] = 'l';
         break;
     case S_IFREG:
         perm[0] = '-';
         break;
     case S_IFBLK:
         perm[0] = 'b';
         break;
     case S_IFDIR:
         perm[0] = 'd';
         break;
     case S_IFCHR:
         perm[0] = 'c';
         break;
     case S_IFIFO:
         perm[0] = 'p';
         break;
     default:
         perm[0] = '?';
         break;
     }

     if (fileStat.st_mode & S_IRUSR)
         perm[1] = 'r';
     if (fileStat.st_mode & S_IWUSR)
         perm[2] = 'w';
     if (fileStat.st_mode & S_IXUSR)
         perm[3] = 'x';
     if (fileStat.st_mode & S_IRGRP)
         perm[4] = 'r';
     if (fileStat.st_mode & S_IWGRP)
         perm[5] = 'w';
     if (fileStat.st_mode & S_IXGRP)
         perm[6] = 'x';
     if (fileStat.st_mode & S_IROTH)
         perm[7] = 'r';
     if (fileStat.st_mode & S_IWOTH)
         perm[8] = 'w';
     if (fileStat.st_mode & S_IXOTH)
         perm[9] = 'x';
 }