The 'simplest' file record structure is the fixed size field .... think IBM, think COBOL; but it IS wasteful if only a few records approach maximum size.

The second simplest alternative is delimited fields, such as CSV ( comma separated values ). It is simplest is there is an ASCII value you can guarantee does not appear in a field, only as a delimiter. Even in XML, you have to guarantee the absence of > & <.

The third solution is to accept that your temporary solution will still be in use 37 years from now, and spec an SQL DB for your data storage.

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