Explanation and Code

The EnumUsers function loops through each user available on the system by using the Net functions. Once data has been recieved, it is converted into a multibyte string and printed to the console. After it has been printed, the next user is grabbed and the loop restarts. Once the loop fails, the function ends with no return value.

#include <windows.h>
#include <lmaccess.h>
#include <iostream>

#pragma comment( lib, "netapi32.lib" )

using namespace std;

// EnumUsers: enumerates the users that may use this system
void EnumUsers()
{
 // variables
 NET_DISPLAY_USER* ndu;
 DWORD entRead;
 int maxForLoop = 0;
 int err;
 char buff[80];
 
 // print info
 cout << "Enumerating users..." << endl;

 // enumerate the users
  // initialize err to get the data
  err = NetQueryDisplayInformation( NULL, 1, 0, 500, sizeof( NET_DISPLAY_USER ), &entRead, (PVOID*) &ndu );
  while( err == ERROR_MORE_DATA )
  {
   // convert the name to a multibyte string
   wcstombs( buff, ndu->usri1_name, GNLEN );
   // output it
   cout << buff << endl;
   // set error to the return value of the function
   err = NetQueryDisplayInformation( NULL, 1, ndu->usri1_next_index, 500, sizeof( NET_DISPLAY_USER ), &entRead, (PVOID*) &ndu );
  }
}

int main()
{
	EnumUsers();

	return 0;
}

(blanked out for safety)