How to retrieve the user name from the user ID

c unix system-calls file-descriptor stat
CompilingCyborg picture CompilingCyborg · Nov 25, 2011 · Viewed 15.7k times · Source

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 the (-l) flag, I see that I have to prompt the user and group names of the file. So far I have the user and group IDs from the following lines: 

struct stat statBuf;

statBuf.st_uid; //For the user id. 
statBuf.st_gid; //For the group id.

In the default (ls) command on Unix, the information of the file is printed in such a way that the user name is shown instead of the user id.

Can anyone help me to find the correct methodology to retrieve the user and group names from their IDs?

Answer

Donal Fellows picture Donal Fellows · Nov 25, 2011

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.

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