fm REUSE_ALV_FIELDCATALOG_MERGE

fm REUSE_ALV_FIELDCATALOG_MERGE

how do I use this fm with my internal report structure?

DATA: BEGIN OF gt_tmp OCCURS 0,

xblnr TYPE char40,
budat TYPE char40,

......

DATA END OF gt_tmp.

but using the "type" because all fields must be char40 and not like a field