How to get file's owner name in Linux using C++?

Question

How can I get get the owner name and group name of a file on a Linux filesystem using C++? The stat() call only gives me owner ID and group ID but not the actual name.

-rw-r--r--.  1 john devl  3052 Sep  6 18:10 blah.txt

How can I get 'john' and 'devl' programmatically?

Answer 1

Use getpwuid() and getgrgid().

#include <pwd.h>
#include <grp.h>
#include <sys/stat.h>

struct stat info;
stat(filename, &info);  // Error check omitted
struct passwd *pw = getpwuid(info.st_uid);
struct group  *gr = getgrgid(info.st_gid);

// If pw != 0, pw->pw_name contains the user name
// If gr != 0, gr->gr_name contains the group name