Code to read users from Active Directory groups and insert in in SharePoint groups

if we want to read active directory users from an active directory group and placed them inside a SharePoint grou, then check below link....

http://www.codeproject.com/KB/sharepoint/Sharepoint__User.aspx

Above link checks if the user exists in active directory. we can modify it  to read users from an active directory group placed inside a SharePoint group.

public DataTable getUsersListFromSPGroup(SPWeb currentWeb, string groupName)
{
bool reachedMax = false;
DataTable dtUsers = new DataTable();
dtUsers.Columns.Add("UserName");
dtUsers.Columns.Add("LoginName");

// The Run with elevated privileges needs read permission
// on active directory and the ability to run directory code.
// We are using RunWithElevatedPrivileges instead of impersonation since we have to access Active Directory
SPSecurity.RunWithElevatedPrivileges(delegate
{
// Get the Site Collection
using (SPSite site = new SPSite(currentWeb.Site.ID))
{
// Get the web
using (SPWeb web = site.OpenWeb())
{
// Find the group
SPGroup group = site.RootWeb.SiteGroups[groupName];

// Get ad users in the groups. Since MOSS does not support nested groups
// this will always be a collection of AD users and groups
foreach (SPUser user in group.Users)
{
// Check if this is a Group
if (!user.IsDomainGroup)
{
if (user.Name.ToUpper() != "SYSTEM ACCOUNT")
{
DataRow userRow = dtUsers.NewRow();
userRow["UserName"] = user.Name;
userRow["LoginName"] = user.LoginName;
dtUsers.Rows.Add(userRow);
}
}
else
{
// If the AD entitiy is a User Group, then check for users in that group
// SPUtility call to get principals in the group
SPPrincipalInfo[] principals = SPUtility.GetPrincipalsInGroup(web, user.LoginName, 500, out reachedMax);
// If no principals found then indicate the same
if (principals != null && principals.Length != 0)
{
// Loop through principals
foreach (SPPrincipalInfo principal in principals)
{
//TODO: Determine which principal.PrincipalType to ignore
// Check if the principal is a valid user and if so check to see if it is
//the one we are looking for
//SPPrincipalType is USER and ignoring All, DistributionList, None, SecurityGroup, SharePointGroup
if (!principal.IsSharePointGroup && principal.PrincipalType == SPPrincipalType.User && principal.DisplayName.ToUpper() != "SYSTEM ACCOUNT")
{
DataRow userRow = dtUsers.NewRow();
userRow["UserName"] = principal.DisplayName;
userRow["LoginName"] = principal.LoginName;
dtUsers.Rows.Add(userRow);
}

}
}

}
}
}
}

});
return dtUsers;
}


And this from the above article.
public bool IsUserInSharePointGroup(SPWeb currentWeb, string groupName, string username)
{
bool reachedMax = false;
bool userIsInGroup = false;
// return false if there are invalid inputs
if (String.IsNullOrEmpty(username) String.IsNullOrEmpty(groupName))
return false;
// The Run with elevated privileges needs read permission
// on active directory and the ability to run directory code.
SPSecurity.RunWithElevatedPrivileges(delegate
{
try
{
// Get the Site Collection
using (SPSite site = new SPSite(currentWeb.Site.ID))
{
// Get the web
using (SPWeb web = site.OpenWeb())
{
// Find the group
SPGroup group = site.RootWeb.SiteGroups[groupName];
string upperCaseUserName = username.ToUpper();
// Get ad users in the groups. Since MOSS does not support nested groups
// this will always be a collection of AD users and groups
foreach (SPUser user in group.Users)
{
// Check if this is a Group
if (!user.IsDomainGroup)
{
// Verify if the user name matches the user name in group
if (user.LoginName.ToUpper().Equals(upperCaseUserName))
{
// if a match is confirmed, return from the method.
// There is no need to continue
userIsInGroup = true;
break;
}
}
else
{
// If the AD entitiy is a User Group, then check for users in that group
if (IsUserInADGroup(web, user.LoginName, username, out reachedMax))
{
userIsInGroup = true;
break;
}
}
}
}
}
}
catch (Exception ex)
{
//Trace error
}
});
return userIsInGroup;
}

private static bool IsUserInADGroup(SPWeb web, string groupName, string username, out bool reachedMax)
{
// SPUtility call to get principals in the group
SPPrincipalInfo[] principals = SPUtility.GetPrincipalsInGroup(web, groupName, 500, out reachedMax);
// If no principals found then indicate the same
if (principals == null principals.Length == 0)
{
return false;
}
else
{
// Loop through principals
string upperCaseUserName = username.ToUpper();
foreach (SPPrincipalInfo principal in principals)
{
//TODO: Determine which principal.PrincipalType to ignore
// Check if the principal is a valid user
// and if so check to see if it is
//the one we are looking for
if (!principal.IsSharePointGroup && principal.PrincipalType
!= SPPrincipalType.SecurityGroup &&
principal.DisplayName.ToUpper() != "SYSTEM ACCOUNT")
{
// Check if the user matches the user we are looking for
if (principal.LoginName.ToUpper() == upperCaseUserName)
{
return true;
}
}
// If Principal is a Security Group (AD Group) then recurse through it
else if (principal.PrincipalType == SPPrincipalType.SecurityGroup)
{
// Check for users in the security groups
if (IsUserInADGroup(web, principal.LoginName, username, out reachedMax))
{
return true;
}
}
}
return false;
}
}