How to retrieve the user name from the user ID

Question

I am implementing the (ls) command on Unix while learning from a book. During the coding part of my implementation of the (ls) command with

Answer 1

check my code for username:

#include <unistd.h>
#include <sys/types.h>
#include <pwd.h>

string getUser(uid_t uid)
{
    struct passwd *pws;
    pws = getpwuid(uid);
        return pws->pw_name;
}

for groupname you can use getgrgid.

Answer 2

You use getpwuid to look up the password file entry for a particular UID (which includes the user name, but now not the password itself) and getgrgid to look up the group file entry for a particular GID.