Problem - Kevin Tafuro

The group structure that is returned by either getgrnam( ) or getgrgid( ) contains a
field called gr_mem that is an array of strings containing the names of all the member
users. The last element in the array will always be a NULL pointer. Determining
whether a user is a member of a group is a simple matter of iterating over the elements
in the array, comparing each one to the name of the user for which to look:
#include
#include
#include
int spc_group_ismember(char *group_name, char *user_name) {
int i;
struct group *gr;
if (!(gr = getgrnam(group_name))) {
endgrent( );
return 0;
}
for (i = 0; gr->gr_mem[i]; i++)
if (!strcmp(user_name, gr->gr_mem[i])) {
endgrent( );
return 1;
}
endgrent( );
return 0;
}
8.3 Getting User and Group Information on
Windows
Problem
You need to discover information about a user or group, and you have a username or
user ID or a group name or ID.
Solution
Windows identifies users and groups using security identifiers (SIDs), which are
unique, variably sized values assigned by an authority such as the local machine or a
Windows NT server domain. Functions and data structures typically represent users
and groups using SIDs, rather than using names.
The Win32 API provides numerous functions for manipulating SIDs, but of particular
interest to us in this recipe are the functions LookupAccountName( ) and
LookupAccountSid( ), which are used to map between names and SIDs.
Getting User and Group Information on Windows | 375
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