Why does my indexed file not have a file header?

Problem:

According to the documentation indexed files should have a 128 byte file header and a record header.

A customer sent us a demo converting an line sequential file to an index file which had no header.

Resolution:

There is always a header in the index portion of the file (assuming the file is not IDX-8)

The 128 byte header referred to in the File Structure docs is in the data portion and only in MF format files.  C-ISAM files do not have a header in the data portion.

Changing the demo to create the output file as variable length altered the output file to include a header.  Running rebuild -f on the file shows it to be MF format IDX-3.

Running the rebuild -f on the original file showed that it was c-isam where the data portion is just a fixed length text file.