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Arrays of Strings in Binary Table Extensions

The definition of the FITS binary table extension format does not provide a simple way to specify that a character column contains an array of fixed-length strings. To support this feature, FITSIO uses a local convention for the format of the TFORMn keyword value of the form 'rAw' where 'r' is an integer specifying the total width in characters of the column, and 'w' is an integer specifying the (fixed) length of an individual unit string within the vector. For example, TFORM1 = '120A10' would indicate that the binary table column is 120 characters wide and consists of 12 10-character length strings. This convention is recognized by the FITSIO subroutines which read or write strings to binary tables.

In early 1993, the WGAS Fits Committee (WFC, the North American committee which reviews changes to the FITS standard) approved a new draft of the Binary Table definition document which contains an appendix describing an alternate convention for specifying arrays of fixed or variable length strings in a binary table character column. This appendix was not officially voted on by the WFC and hence is still provisional. FITSIO does not yet support this new proposal, but this will probably be added in a future release of FITSIO.