How do I add permissions to my ls-al c program? - c

Question

I am writing code to implement the ls-al command using c program and I have gotten my code to implement it without printing permissions but I want to implement the permissions as well but cant figure out how. any suggestions? my code is below
#include <stdio.h>
#include <stdlib.h>
#include <dirent.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <time.h>
#include <pwd.h>
// Last Modified
time_t t = my_stat.st_mtime;
localtime_r(&t, &lt);
char timebuf[80];
strftime(timebuf, sizeof(timebuf), "%c", &lt);
if (pwd != 0) {
printf("%s \t %ld \t %s \t %s", pwd->pw_name, (long)my_stat.st_size, timebuf, current_directory->d_name);
printf("\n");
} else {
printf("%d \t %ld \t %s \t %s", my_stat.st_uid, (long)my_stat.st_size, timebuf, current_directory->d_name);
printf("\n");
}
}
closedir(directory);
return 0;
}
int main(int argc, char* argv[]) {
if ( argc == 1 ) {
return list_dir ( "." );
} else {
int ret = 0;
for (int i = 1; i < argc; i += 1 ) {
if ( list_dir ( argv[i] ) != 0 ) {
ret = 1;
}
}
return ret;
}
}
I have ben trying for a long time to be able to add permissions to this code but I seem to be getting stuck and am out of ideas here
the output of my code is:
kev 0 Thu Jun 20 13:39:49 2019 .
kev 0 Thu Jun 20 13:39:46 2019 ..
kev 24147 Thu Jun 20 12:24:40 2019 CMakeCache.txt
kev 0 Thu Jun 20 13:39:53 2019 CMakeFiles
kev 1426 Thu Jun 20 12:24:41 2019 cmake_install.cmake
kev 5160 Thu Jun 20 12:24:41 2019 Makefile
the expected output is:
rw-r--r-- 1 kev 0 Thu Jun 20 13:39:49 2019 .
rw-r--r-- 1 kev 0 Thu Jun 20 13:39:46 2019 ..
-rw------- 24147 Thu Jun 20 12:24:40 2019 CMakeCache.txt
rw-r--r-- kev 0 Thu Jun 20 13:39:53 2019 CMakeFiles
-rw------- kev 1426 Thu Jun 20 12:24:41 2019 cmake_install.cmake
rw-r--r-- kev 5160 Thu Jun 20 12:24:41 2019 Makefile

Answer 1

You will want to make use of the mode_t st_mode field of your struct stat. See stat(2):
The stat structure
All of these system calls return a stat structure, which contains the following fields:
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; /* blocksize 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 };
[...]
The file type and mode (st_mode)
POSIX refers to the st_mode bits corresponding to the mask S_IFMT (see below) as the file type, the 12 bits corresponding to the mask 07777 as the file mode bits and the least significant 9 bits (0777) as the file permission
bits.
The following mask values are defined for the file type of the st_mode field:
S_IFMT 0170000 bit mask for the file type bit field
S_IFSOCK 0140000 socket
S_IFLNK 0120000 symbolic link
S_IFREG 0100000 regular file
S_IFBLK 0060000 block device
S_IFDIR 0040000 directory
S_IFCHR 0020000 character device
S_IFIFO 0010000 FIFO
[...]
The following mask values are defined for the file mode component of the st_mode field:
S_ISUID 04000 set-user-ID bit
S_ISGID 02000 set-group-ID bit (see below)
S_ISVTX 01000 sticky bit (see below)
S_IRWXU 00700 owner has read, write, and execute permission
S_IRUSR 00400 owner has read permission
S_IWUSR 00200 owner has write permission
S_IXUSR 00100 owner has execute permission
S_IRWXG 00070 group has read, write, and execute permission
S_IRGRP 00040 group has read permission
S_IWGRP 00020 group has write permission
S_IXGRP 00010 group has execute permission
S_IRWXO 00007 others (not in group) have read, write, and execute per‐
mission
S_IROTH 00004 others have read permission
S_IWOTH 00002 others have write permission
S_IXOTH 00001 others have execute permission