I’m working on a data-migration scenario, where there is a need to update the CreatedBy (Author) and ModifiedBy(Editor) fields in SharePoint.

            using (SPSite oSPSite = new SPSite(http://yoursitecollectionurl))
            {
                using (SPWeb oSPWeb = oSPSite.RootWeb)
                {
                    SPList oSPList = oSPWeb.Lists["testlist"];


                    foreach (SPListItem oSPListItem in oSPList.Items)
                    {
                        SPFieldUserValue oSPFieldUserValue = new SPFieldUserValue(oSPWeb, oSPWeb.AllUsers[@"domainuser"].ID, 

                           oSPWeb.AllUsers[@"domainuser"].LoginName);

                        oSPListItem["Author"]= oSPFieldUserValue;
                        oSPListItem["Editor"]= oSPFieldUserValue;
                        oSPListItem.Update();                      

                                        }
                
                } 

The above code-snippet updates the Author and Editor fields of SharePoint list, based on the specific user (SPFieldUserValue object).

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