Getting uid and/or username of logged in user

rjstephens · 09-22-2004, 02:36 AM

Hi
I am writing a C++ app and i need a way to get the the user ID and the user name of the currently logged in user. Any ideas?

(BTW, this is on linux)

Cedrik · 09-22-2004, 03:34 AM

man utmp

rjstephens · 09-22-2004, 03:38 AM

thanks.

rjlee · 09-22-2004, 03:41 AM

If you mean that you want the username and ID of the user who is running the program, you can use

Code:

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

uid_t uid getuid(void);

You can pass this uid value to getpwdnam to return a structure representing the password file entry:

Code:

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

struct passwd pw *getpwuid(uid);

And then read out the username with the pw_name field pointed to by pw.

You can also get the username of the current user (which may or may not be either the logged in user or the user running the process; see su -m) using

Code:

#include <stdlib.h>

char * uname = getenv("USER");

I hope that's legible,

— Robert J. Lee

rjstephens · 09-22-2004, 03:50 AM

thankyou rjiee, I am using:

Code:

#include <unistd.h>

int uid = getuid();

That appears to work. "void" gives a parser error for some reason (I'm using g++). I'll get to the user name stuff later, I don't need that just yet.

Cedrik, thanks but I was just searching on google for details of how to get that to work. Couldn't find any, then I saw rjiee suggestion. Thanks anyway.

rjlee · 09-23-2004, 05:02 PM

void is only allowed in function prototypes in C or C++. It just means that no parameter is allowed (and can sometimes be omitted).