LinuxQuestions.org - Getting the owner name of a file in C

- Programming (https://www.linuxquestions.org/questions/programming-9/)

- - Getting the owner name of a file in C (https://www.linuxquestions.org/questions/programming-9/getting-the-owner-name-of-a-file-in-c-165250/)

Getting the owner name of a file in C

I am writing a function works like "ls -l".

How can i get the owner name of a file?
I only know how to get the owner id from "lstat", is there a function convert the uid to user name?

And also how can i print out the permission in this format "drwxr-xr-x"?

This is what my code looks like so far:

Code:

void dir(char *dir_name)

{

  DIR *dirStream = NULL;

  struct dirent  *dirEntry  = NULL;

  struct stat    buf;

  

  if ( (dirStream=opendir(dir_name)) == NULL ) {

      printf("%s: error while opening the directory\n",dir_name);

    return;

  }



  while((dirEntry = readdir(dirStream)) != NULL) {

    if ( strcmp(dirEntry->d_name,".")!=0 && strcmp(dirEntry->d_name,"..")!=0 ) {

      lstat(dirEntry->d_name,&buf);

      

      printf("%d",buf.st_uid);

      printf("\t%d",buf.st_size);

      printf("\t%s",dirEntry->d_name);

                

      if (buf.st_mode & S_IFDIR)

        printf("/");



      puts(""); // newline

    }

  }



  return;

}

Quote:

Originally posted by Hko
See "man getpwuid"

Thanks.

How about...
Do you know how to print the permissions like that?

Use stat(), fstat(), or lstat() on the file/directory. Then check the st_mode member of the "struct stat" , which is filled by stat(), against all bitmasks to decide what character ( '-', 'r', 's', 'x', 'S' ....) to print. Like so:

Code:

if (status.st_mode & S_IRUSR) {

    /* owner has read permission */

    /* print corrosponding character in correct position */

}

It's probably best to check in the order you need to print the char's

Quote:

Originally posted by Hko
Use stat(), fstat(), or lstat() on the file/directory. Then check the st_mode member of the "struct stat" , which is filled by stat(), against all bitmasks to decide what character ( '-', 'r', 's', 'x', 'S' ....) to print. Like so:

Code:

if (status.st_mode & S_IRUSR) { /* owner has read permission */ /* print corrosponding character in correct position */ }

It's probably best to check in the order you need to print the char's

Yeah i see. Thank you very much!

This seems to work for me. I'm sure it can be beautified using a loop, but this at least illustrates it (also, I didn't bother looking up the actual letters for the different types of files. I made some of them up):

Code:

#include <stdio.h>

#include <sys/types.h>

#include <sys/stat.h>

#include <unistd.h>



int main(void)

{

  char str[11], *s = str;

  struct stat st;

  mode_t owner, group, other;



  if(lstat("myfile", &st) < 0)

  {

    printf("Couldn't open file.\n");

    return 1;

  }



  if(S_ISREG(st.st_mode))

    *s++ = '-';

  else if(S_ISDIR(st.st_mode))

    *s++ = 'd';

  else if(S_ISCHR(st.st_mode))

    *s++ = 'c';

  else if(S_ISBLK(st.st_mode))

    *s++ = 'b';

  else if(S_ISFIFO(st.st_mode))

    *s++ = 'f';

  else if(S_ISLNK(st.st_mode))

    *s++ = 'l';

  else

    *s++ = 's';



  owner = st.st_mode & S_IRWXU;

  group = st.st_mode & S_IRWXG;

  other = st.st_mode & S_IRWXO;



  *s++ = owner & S_IRUSR ? 'r' : '-';

  *s++ = owner & S_IWUSR ? 'w' : '-';

  *s++ = owner & S_IXUSR ? 'x' : '-';



  *s++ = group & S_IRGRP ? 'r' : '-';

  *s++ = group & S_IWGRP ? 'w' : '-';

  *s++ = group & S_IXGRP ? 'x' : '-';



  *s++ = other & S_IROTH ? 'r' : '-';

  *s++ = other & S_IWOTH ? 'w' : '-';

  *s++ = other & S_IXOTH ? 'x' : '-';



  *s = '\0';



  puts(str);



  return 0;

}