文件I/O实践(2) --文件stat

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';
}

[拓展]

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';
}