#include <sys/stat.h>

    int stat(const char *restrict pathname, struct stat *restrict statbuf);
    int fstat(int fd, struct stat *statbuf);
    int lstat(const char *restrict pathname, struct stat *restrict statbuf);

DESCRIPTION
    These functions return information about a file, in the buffer
    pointed to by statbuf.  No permissions are required on the file
    itself, but—in the case of stat(), fstatat(), and lstat()—execute
    (search) permission is required on all of the directories in
    pathname that lead to the file.

RETURN VALUE
    On success, zero is returned.  On error, -1 is returned, and
    errno is set to indicate the error.

#include <sys/stat.h>

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 512 B blocks allocated */

    /* Since POSIX.1-2008, this structure supports nanosecond
        precision for the following timestamp fields.
        For the details before POSIX.1-2008, see VERSIONS. */

    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
};

#define S_IFMT (0xF000)
/* 判断原理就是拿 m 的高 4bits 与高 4bits 全 1 的 mask 值进行与运算后，与各个文件类型的定义进行比较 */
#define	S_ISDIR(m)	(((m) & S_IFMT) == S_IFDIR) // 判断文件是否是一个 directory
#define	S_ISFIFO(m)	(((m) & S_IFMT) == S_IFIFO) // 判断文件是否是一个 named FIFO pipe
#define	S_ISCHR(m)	(((m) & S_IFMT) == S_IFCHR) // 判断文件是否是一个 character device
#define	S_ISBLK(m)	(((m) & S_IFMT) == S_IFBLK) // 判断文件是否是一个 block device
#define	S_ISREG(m)	(((m) & S_IFMT) == S_IFREG) // 判断文件是否是一个 regular file

/* 使用示例 */
int ret_code;
struct stat st;

ret_code = stat(path, &st);
assert(ret_code, 0);
S_ISREG(st.st_mode); // 判断文件是否是一个 regular file

#define S_IRWXU  00700 // owner has read, write, and execute permission
#define S_IRUSR  00400 // owner has read permission
#define S_IWUSR  00200 // owner has write permission
#define S_IXUSR  00100 // owner has execute permission

#define S_IRWXG  00070 // group has read, write, and execute permission
#define S_IRGRP  00040 // group has read permission
#define S_IWGRP  00020 // group has write permission
#define S_IXGRP  00010 // group has execute permission

#define S_IRWXO  00007 // others (not in group) have read, write, and execute permission
#define S_IROTH  00004 // others have read permission
#define S_IWOTH  00002 // others have write permission
#define S_IXOTH  00001 // others have execute permission

/* 使用示例，判断是否具有执行权限 */
if ((st.st_mode & S_IXUSR) || (st.st_mode & S_IXGRP) || (st.st_mode & S_IXOTH)) { }