Function TupleDescInitEntry

src/backend/access/common/tupdesc.c:590–657

* TupleDescInitEntry * This function initializes a single attribute structure in * a previously allocated tuple descriptor. * * If attributeName is NULL, the attname field is set to an empty string * (this is for cases where we don't know or need a name for the field). * Also, some callers use this function to change the datatype-related fields * in an existing tupdesc; they pass attribut

 * TupleDescInitEntryCollation.
 */
void
TupleDescInitEntry(TupleDesc desc,
				   AttrNumber attributeNumber,
				   const char *attributeName,
				   Oid oidtypeid,
				   int32 typmod,
				   int attdim)
{
	HeapTuple	tuple;
	Form_pg_type typeForm;
	Form_pg_attribute att;

	/*
	 * sanity checks
	 */
	AssertArg(PointerIsValid(desc));
	AssertArg(attributeNumber >= 1);
	AssertArg(attributeNumber <= desc->natts);

	/*
	 * initialize the attribute fields
	 */
	att = TupleDescAttr(desc, attributeNumber - 1);

	att->attrelid = 0;			/* dummy value */

	/*
	 * Note: attributeName can be NULL, because the planner doesn't always
	 * fill in valid resname values in targetlists, particularly for resjunk
	 * attributes. Also, do nothing if caller wants to re-use the old attname.
	 */
	if (attributeName == NULL)
		MemSet(NameStr(att->attname), 0, NAMEDATALEN);
	else if (attributeName != NameStr(att->attname))
		namestrcpy(&(att->attname), attributeName);

	att->attstattarget = -1;
	att->attcacheoff = -1;
	att->atttypmod = typmod;

	att->attnum = attributeNumber;
	att->attndims = attdim;

	att->attnotnull = false;
	att->atthasdef = false;
	att->atthasmissing = false;
	att->attidentity = '\0';
	att->attgenerated = '\0';
	att->attisdropped = false;
	att->attislocal = true;
	att->attinhcount = 0;
	/* attacl, attoptions and attfdwoptions are not present in tupledescs */

	tuple = SearchSysCache1(TYPEOID, ObjectIdGetDatum(oidtypeid));
	if (!HeapTupleIsValid(tuple))
		elog(ERROR, "cache lookup failed for type %u", oidtypeid);
	typeForm = (Form_pg_type) GETSTRUCT(tuple);