Salesforce Database.saveResult and Database.Error example

Code snippet :

List<Contact> con = [select id,lastname,AccountId from contact order by createddate desc Limit 20];
//Map<Id,Contact> conAcc = new Map<Id,Contact>();
Set<Id> conSet = new Set<Id>();
for(contact conn : con){
    if(String.isNotBlank(conn.AccountId)){
        conSet.add(conn.AccountId);
    }
}
Map<Id,Account> conAcc = new Map<Id,Account>([select Id,name from account where Id IN : conSet]);
for(contact connn :con){
    if(conAcc.containsKey(connn.AccountId)){
        connn.lastname = connn.lastname +'--'+ conAcc.get(connn.AccountId).name;
    }
}
Database.SaveResult[] res = database.update(con,false);
List<Database.Error> dError = new List<Database.Error>();
system.debug(res);
for(Database.SaveResult result :res){
    if(result.isSuccess()){
        system.debug('Pass--->>'+result.getId());
    }else{
        system.debug('faled--->>'+result.getErrors());
        dError.addAll(result.getErrors());       
    }
}
for(Database.Error r : dError){
    system.debug('Fields ---->>>'+r.getFields());
    system.debug('Messages ---->>>'+r.getMessage());
    system.debug('Status Code ---->>>'+r.getStatusCode());

}