Transfer file string to Dataset

I have a program which transfers inbound IDOC file from local directory to the application server. I stored the file contents to an internal table with a single field type STRING. The file has a maximum of 541 chars per row. But when I transferred each row, only the first 256 chars were transferred to the file in the application server. How will I transfer the whole string?

Below is a snipet of the code:

DATA: gc_fname TYPE authb-filename.

DATA: BEGIN OF gt_file OCCURS 1000,

str TYPE STRING,

END OF gt_file.

OPEN DATASET gc_fname FOR OUTPUT IN TEXT MODE

ENCODING DEFAULT.

IF sy-subrc EQ 0.

LOOP AT gt_file.

TRANSFER gt_file-str TO gc_fname LENGTH 541.

ENDLOOP.

ENDIF.

CLOSE DATASET gc_fname.