What the function name to get the contents table/tuple ?

Using this code below (particularly heap_open) somehow i can fetch all
table column name, and put in on list of string. Before raw_parsetree is
processed by analyze part.

------start code ----------------
---------------------------------

RangeVar *relation = makeNode(RangeVar);                 relation->schemaname = NULL;
relation->catalogname= NULL;               relation->relname = "pg_class"; //table name               relation->inhOpt
=INH_DEFAULT;                relation->istemp = false ;               relation->alias = NULL;
 

Relation Rel;
LOCKMODE            lockmode = AccessShareLock;

Rel = heap_open(TableSpaceRelationId,lockmode);
Value               *attrname ;
TupleDesc           td;
td = Rel->rd_att;

List                *colnames;
colnames = NIL;
int                 z;
int                 maxatribut = td->natts;
Form_pg_attribute   fpa;

for (z=0;z<maxatribut;z++) {   fpa       = td->attrs[z];   attrname  = makeString(pstrdup(NameStr(fpa->attname)));
colnames = lappend(colnames,attrname); //this where list cols name
 
colected }

------end code ----------------
---------------------------------

My question, is there same kind function that i can use to get table
content (tuple)?

Thank You.
-- 
Mohammad Heykal Abdillah <heykal.abdillah@gmail.com>