How to map UID/GID to username/groupname in linux

Question

In a C program on Linux, I get UID and GID of a file, but I want to print the username and group name. So how to map UID/GID to username/group name?

Answer 1

Use the getpwuid function to get the username associated with a uid:

struct passwd *getpwuid(uid_t uid);

The name is returned in passwd.pw_name

For groups, use getgrgid :

struct group *getgrgid(gid_t gid);

The name is returned in group.gr_name